Defiantly a cool idea and one that's been passed along before. The primary factor and issue preventing being, even with this pretty reasonable breakdown above, its actually even more complicated than that. Sometimes work on a particular vehicle could have started initially in the planning stage 2 years before its actually introduced. Then its could be museum trips, archive visits, book / source acquisition and a lot of elements where the part most people would find interesting would effectively stop for a while and then pop back up. Its not impossible, but it could quite literally take a year from start to finish to make ))
What I could do at least is perhaps do a few small articles here on the forum detailing a bit more about some of the museums we have been to (at least trips I've been on and have the photos to share) for vehicles already in game and talk about that side of the process, the museums / places and how we got to the end result on several aircraft. But that's a much more cut down, all be it easier to actually create snip of what you were actually suggesting.
Once we hit the SEP end of the spectrum, US tanks are effectively done. Sep V3 and 4 are on the complete upper end closer to Challenger 3 levels of nigh impracticality at the current stage. Japan has only just received the Type 10 for example after a considerably long wait after the Type 90(B). We explained in detail why this was, being a mixture of lack of the detailed information we needed to model it and also with the fact the Type 90s themselves were not doing overall poorly and not at the bottom of their performance bracket. As well as the fact the Type 10 would effectively be the end of the road for Japanese MBTs.
Indeed, the US does have more to chose from in this department. But it is again reaching the upper echelons of what's possible with the M1A2 itself having a very strong surrounding line-up, which is also and important consideration to factor in, rather than just going X nation has X MBT but Y has this MBT and this MBT.
More US vehicles are coming, as we have explained in the past, they always have and always will have more to add than most other nations. But with that comes proper content deployment.