Yeah, much as I hate to agree with IL… :-D…
I think you’re tanks would be fine if they looked right next to AA tanks, but they are too big for AA and not detailed enough for the hardcore tactical wargamer types. As some others mentioned, they might work with other plastic-based games, like ToI or Memoir '44, but I’m no expert on that. You’re best bet is probably to do like you were saying and create your own game to go with them, though such a game is unlikely to require French or Hungarian units, since more tactical-level games focus on the “big guys” and more iconic, late-war tank models, especially US, UK, German and Soviet models. I’m not sure what sort of game would include Japanese and Italian units at the same time, but then I’m still glad you’re making those two countries, as I just think they’re cool, so I want to get at least one set of each to show my support and possibly come up with a use for later. So I’ll definitely pick up your Japanese set and I am eagerly awaiting your Soviet set, even if I haven’t decided what I’m going to do with it just yet, long term.
I probably will use your the Cromwells and Pershings until I have an alternative heavy-tank option for the US and the UK and continue to use TWG pieces for the German heavy tanks until I find something better. When your Soviets come out, I hope they include a JS2, and if they do, that will become my provisional Soviet heavy tank. (Do Italy and Japan even really need one? Well, if they do, I already have your Italians and will get your Japanese…) But I’m going to hold off on making a really big purchase to replace all of the A&A tanks in my top-shelf AAA set until I see what all the options will be after I have a clearer picture of what your proposed in-scale A&A set will be and also what FMG is going to offer.