Man, I won't sit here and tell you "Hurr durr, just buy another PC," but chances are, if you're playing PokeMMO right now, you have a decent enough PC to play it post-Unova. When the first PTS came out for it, my craptop with Windows 7 Home, 4GB RAM, an outdated i3 processor, and (laugh while I'm giving you the opportunity) Intel HD 3000 Graphics card in it, which has a grand total of 64MB of dedicated VRAM. This piece of heck laptop still played PokeMMO PTS with no issues in terms of 3D rendering and smoothness. As Desu and Xela have stated before: From a developer's standpoint, it makes no sense to cater to a very small amount of people that might not have 1.5GB of RAM on their computers or a graphics card that isn't compatible with OpenGL 2.0 or higher. (lul)
Chances are is that if you can currently play PokeMMO as it is, you will be able to play post-Unova.