I came across this article - How to get that old-fashioned light bulb glow without wasting so much energy.  It sounds like a more advanced infrared reflective coating.

Well, these structures will be exposed to the full filament heat (so the grains will suffer from internal stresses and consequently cracking or so), yet the performance will be very sensitive for the ability to maintain the critical parameters (grain size).
So I would expect rather fast lumen depression of the resulting lamps - just because the IR conserving structures will degrade.
And still, there would remain the rather high principal losses (gas fill and consequent bulb heating, shorter wave IR radiation,...), quite high sensitivity for the supply parameters (so most likely it will require a power stabilizing ballast, so not that simple as the classical incandescent), so I don't think it would become competitive for a general lighting applications. Of course, some for some special applications it may work pretty well.

By the way by just using tightly regulated supply on a classic incandescents you may gain about 20% extra light for the same life rating. Just because of better control of the filament temperature, so I doubt such complex lamp will be ever intended to work without such regulator.

Not just a phase-angle "dimmer" in the base ?

Not just a phase-angle "dimmer" in the base ?

It would be quite complex stuff: Using a phase angle keep the rms lamp voltage constant. Not much feasible without some microcontroller or so.
But there is more severe problem with such thing: The mains current harmonic content limits are way too strict for such concept to pass.
And I'm not sure, if such thing could be applied on so thin filament as used with mains voltage lamps. Don't forget for general lighting with efficacy above 50..100lm/W (that would be necessary to be able to compete with the LED's) we are talking about power levels of 20W or below. That means resistances above 500Ohm for 120V mains, so really quite thin and long filament. And that already hase structural problems carrying it's own weight inside classic incandescents, here it will have to carry the weight of the coat, so becoming even more fragile.
So from that perspective I would expect such technology to be usable only on either ELV lamps (with rather short, thick filaments) or really high power lamps.

The only usage I may imagine in car front lighting (being lightweight, yet efficient), but the real fuel consumption related to front lighting is not the top priority today (otherwise the industry would stick with halogens - as they are the system with lowest mass and the mass is responsible for way greater impact on the fuel economy than the lamp efficacy). The priority is shifted towards the ability to shape the beam, so it may reach far distance and still avoid glare of the other traffic. And for that you need individual control of many small beam sections. And that suits only the LED's and/or laser systems, where the downscaling of the individual light segments does not impair the efficacy, as it does with the "classic" technologies.
But I may expect there for sure will be applications for these, where the special ballast would be justified.

How about all the 12V halogen/LED downlighters ? Just replace the "ringing circuit" converter to a stabilized PS

On 12V the wiring voltage drop uses to be quite significant.
And mainly I would expect even the present LED's to be cheaper and way more reliable than such thing.
I would really expect the main use would be in measurement instruments (some specrometers for material analysis,...), where really a smooth continuum is required to not mess up the measurement results.

With 100 Lm/W there is not as much current draw, so not as much voltage drop. Besides, the power supply can be made as a constant current driver (and if multiple lamps then connect them in series, up to 4 lamps = 48v per circuit), then wire voltage drop won't affect the driving of lamps at all

I am coming to this from the perspective of eliminating LEDs in all general purpose lighting on account of their output spectrum, so this lamp looks like viable solution even if it is more expensive

At the time this will really reach the market as a real product with efficacy just around 100lm/W, the LED's will be in the 80..90% energy efficiency range, that means 200..300lm/W depending on the color quality. And because for practically all duties the present color quality of the (real) 80+ CRI is way sufficient, I don't think there would be any rush for such not that reliable and expensive infant thing with no prospect becoming significantly better in that, in times when the LED and/or laser based systems will be very mature technology offering triple efficacy and way lower cost.
That is, why I see the main use only in areas, where the guaranteed smooth continuum is a must, so what the narrow band nature of the high efficient energy quantum based light sources (LED's, lasers,...) can never really guarantee.

The spectral content of present day LEDs is inadequate for general purpose lighting (and this have little to do with CRI). The rush with the LEDs appears to fucus on getting higher Lm/W alone, but not addressing the spectrum. In fact, i have read about proposals to change the definition of CRI in order to suit it to favor the LEDs

I came across this article - How to get that old-fashioned light bulb glow without wasting so much energy.  It sounds like a more advanced infrared reflective coating.

GE came up with this technology many years ago and licensed it to Toshiba, who has since discontinued their manufacture. Philips makes them now for automotive use in the 9011 and 9012 fitments.

Can this technology be used to improve efficiency of MH lamps? Or even MV lamps for cosmetic purpose?

Can this technology be used to improve efficiency of MH lamps? Or even MV lamps for cosmetic purpose?

Not at all, it is purely about incandescent light emission principle.
The concept is based on a fact, a hot surface radiates mainly on wavelengths such surface absorbs. In other words if a surface color means the filament absorbs in visible range and reflects elsewhere, it will radiate in visible and not elsewhere. And that is the point: If the energy could be radiated only in the visible, all the energy income may leave only as a visible light, so the input energy is converted to the visible with high efficacy.
So it works only in thermal radiation, not with electron energy level transition mode of light generation. So it is only about incandescents.

As such this principle is well known since the "black body" radiation was first described. But the problem is, the required absorbtion/reflection properties should be present at the operating temperature. And that is in the 2500..3000K range. For most of the incandescent history the main problem was to find a way to make the filament so, it will at least survive that temperature for a reasonable lifetime, attempting to alter it's color (so the abrsorbtion/reflection spectra) was considered as far out of the "feasible" range.
There were known ways to form e.g. a ridges forming color selective grating on the metal surface, but these would be very quickly eroded by the normal lamp wear, so not usable for the filament coloring.
I do not know details about this (and the older GE) ways, most likely it would be some ceramic coat or so, maybe even a ceramic filament (Nernst lamp reborn?), the advance in ceramic technologies may allow such creations.
Or even a carbon filament (where the miniature features forming the color are quite easy to make these days), with some ceramic coat protecting the filament from evaporation.

But MH lamps also emit a considerable amount if IR radiation, can that not be used to produce more light?

But MH lamps also emit a considerable amount if IR radiation, can that not be used to produce more light?

This has nothing to do with the spectra, but with the physics, how the light is generated.
It is not any phosphor or so (converting UV to visible on e.g. MV's or some MH's), it is a measure to prevent just an incandescent radiator from radiating outside of the desired spectra.
So because of that it is applicable only on lamps based on incandescence to generate the light.

With the discharges the main spectra is not generated by incandescence at all. The IR is either a thermal radiation of the arctube body (that is too cold to radiate in visible), maybe the electrodes (their function is to emit and collect electrons, the radiation is just a side effect and usually suppressed as much as possible, that dictates how they look like) and/or residual radiation of either gasses or the phosphor (neither of these is incandescence either).