From the very few pictures I was able to find of Rogue Trouper that seems a decent scale in 15mm. It seems like a small tactical scale at the platoon level.
Alright guys were going to figure Matt out before the big unveil
Now here is what we know. Its a 6mm miniature game that starts with R. Not much to go on, or is it? First off Project R narrows things a bit, the number of games and RPG setting that start with R over the past twenty years is quite small. Also there is the 6mm scale. As I said before this would seem to indicate a massive scale. Troops would be about half the size of Flames of War, so were talking pretty small. It would be easy to represent entire companies of Infantry, Brigades of Armor etc.. The next clue is the name Project R**, take note of the R** why didn't Matt just call it Project R? Obviously he could just be messing with us, but more likely that represents something. The Last clue is Matt said this was something they had been working on for a long time and were finally going ahead with. I take this to mean this setting is probably a little obscure and has required a bit of negotiation to track down all the parties involved in its licensing. You will note that I am assuming Mongoose is producing someone Else's license rather than creating an entirely new setting. Lastly its just a gut feeling, but I don't think this will be a fantasy setting for no other reason than there are SO many of those on the market in every scale imaginable.
Alright guessing time...
My top two picks based on all the clues I have mentioned above are.
this was a major hit anime from the early 80's which has a major cult following. No miniature games has ever been done for it, despite a solid number of mecha that could be modeled. However I don't think 6mm is the proper scale for it, perhaps 15 or 20mm.
This is another 80's item, it was produced by FASA and did include a space and ground combat game as well as an interesting RPG. 6mm would work very well for the ground combat component as the military campaign in the setting were quite extensive. Still its an old and almost unknown license to be resurrected so many years later...