Where does the 22 TCM hold any advantage over already available platforms?
Obviously, I will agree ahead of time that the .22 TCM is not going to vie with the Glock 19 or the J-frame .38 for top billing as a defensive handgun. And you probably got it close to "right on" when you hinted that gun cranks who like to play with oddball stuff is the likely target market...
In any case, I think the answer to your question is that the .22 TCM aims to do something similar to the cult-followed 5.7x28mm FN Five seveN pistol. It's a hot .22cal slug going at a very high speed.
Perhaps bettering the 5.7x28 in a couple of ways--
--It's a lower priced platform, and by a HEAP of money
--It's a far more familiar, established, known and loved platform, 1911(ish) rather than SpaceGun looking
--It has the swappability and kit to run multiple calibers right in the box it's shipped with, allowing for the owner to play with and run a double-stack 9mm
For Rock Island to have put that all together and offer it at THIS price point is quite an accomplishment, in my opinion.
But "how is it better than all the established stuff?"
It's likely not. Just like .357 Sig... .327 Federal... .460 Rowland...
and a zillion other ideas and marketable products.