1) Quartz vs Ceramic Chemistries:
I am aware of three major MH chemistries, those being sodium-scandium, sodium-thallium-indium, and dysprosium-thallium-cesium. As far as I am aware these are QMH chemistries. Are different chemistries used for CMH lamps, and if so what are they? I've heard of the early tin-sodium lamps but I am thinking more mainstream.

2) Pros and Cons:
So there's a few different chemistries, what are their pros and cons? I see some MH lamps with vacuum outers and some with nitrogen outers, when is one preferable over the other? Also some MH lamps lack reflective end coatings, when is this necessary?

3) Probe Disconnection:
Most probe-start lamps disable their probes with a bimetallic switch. Typically this is done by shoring the probe to the electrode near it, keeping the resistor in circuit. However I have heard of lamps that actually isolate the probe. Why wouldn't everyone do that? It's wasteful to keep the resistor in circuit.

4) Probe Boosting Circuitry:
According to this lamptech page, GTE Sylvania developed a metal halide lamp which used two resistors and a zener diode to increase the voltage available at the probe. I haven't the slightest idea how this would be at all possible without the use of a capacitor, but I said the same thing for FEC ignitors and I understand them now lol. How does this arrangement work?

Thanks!

Ugh! Your questions worth a rather thick book on MH technique )

Some quick thoughts:

Alumina arc tubes in ceramic MH lamps are less reactive to the filling salts and allow for higher temperatures and pressures. So classic fills like Dy + Tl + Na just work better (due to spectral line widening) but also CMH allows for some unique new metals. Probably the most significant is calcium, which under CMH conditions radiates a few  wide bands in deep red, allowing for creation of CRI 90+ 3000K lamps, finally with a good R9 rating, which usually suffered in other MH lamps, due to inevitable emphasis of Na radiation on orange.

Probe disconnect by a normally closed switch is just mechanically more cumbersome than a simple normally open U-shaped bimetallic strip placed between cathode and probe leads. Look here https://www.lighting-gallery.net/gallery/displayimage.php?pos=-229314 and here https://www.lighting-gallery.net/gallery/displayimage.php?pos=-229361

Probe ballast resistor is a relatively high value, somewhere around of 10 kiloohms, so actual power losses are not especially significant.
Anyway, probe start lamps were a long time obsolete tech many years ago already. All high performance designs are pulse start.