I saw a listing on Ebay for a Philips HGS203 with two lampholders. I had never seen or heard of there being a two lamp version of the HGS203. At first I thought it was something homemode but it seems to have a genuine Philips nameplate that reads ”HGS203/2x50-80” ”2XHPL 80w” ”3K  ML   Made in France”

Does anyone have any more information about this unicorn of a lantern and are there others like it?

That is possibly the weirdest configuration for a 203, that type of reflector is made for Ovoidal lamps, so it isn't usually made for two lamps because of the space between them, and i don't even think the 203 was built for that.

But seeing the fixture itself is brand new in-box and has an actual denomination on the label about its lamp configuration, it would mean it was actually an option on a catalog, or a special configuration of an extremely low demand.

Since "Made in France" is in the label as you said, looking at the French 1983 Philips catalogue (first apparition of the fixture) there is no trace of any "double lamp" option anywhere, nor in the later catalogues. So this is probably either one of a kind or mega extremely rare to come across, or both! 

Wow, that’s one odd lantern then. I know some cities used two bulb street light lanterns for an early kind of dimming / power saving but HGS203 is a really odd choice for that sice as you pointed out, the optics really aren’t optimized for this kind of use. Could this be a prototype of some sort?

Where do you find those old product catalogues by the way? Do you have them in physical form?

I generally use a website for that kind of research: http://phozagora.free.fr/?page=catalog (It's in french so i recommend to use english translation)