I don't see why DCS shouldn't develop other types of airplanes. If they want to develop a WWII simulator, make a better job in this subject than IL-2 series, for me, and surely for many other people, that's great news. I find it pretty healthy to offer different products, as long as they are quality ones. From what I understood, there is the possibility of having a top class P-51D simulator, with realistic flight model, that is able too shoot down other planes, thing that FSX planes can't!!! Come on!! That's just wonderful to know. Specially knowing that the flying simulator market is not very prolific with really good products.
Of course, I agree that as a DCS addon, it would be much more interesting to have several other equally top class developed airplanes to fight with P-51D. And what about if they come up with really good planes from the 50's, 60's and 70's? Wouldn't that be great?!
I find DCS initiative very positive in many ways. I think that developing other kind of planes shouldn't be considered as a negative thing, but a positive one. I don't think they are going to stop developing modern jets. Stay cool and enjoy
Cheers