I'm interested. I tried to join a superpower RP not long ago but the GM retired before it even started.

I'd like to suggest a very basic addition: generally Shifters don't use their powers (to avoid detection, I suppose), but if they use them for an extended period of time their power "branches off" to a slightly different ability. A good example would be Avatar: The Last Airbender, where Toph developed metalbending from extensive training as an earth bender. We can also set it up so that the Shifters do not not know this and either discover it or are told from an older Shifter who has survived. 

It could be as simple as a mild power lasting longer or being more powerful, or as clever as it branching into something knew but connected to the first. After all, there are tons and tons of potential superpowers and isolating only one would be a tough choice. You would have to confirm them, of course, and all initial powers should have a weakness of some kind. It might be necessary, since the government is capable of creating their own Shifters and they could tailor them to defeat people with only one power.

Any of that sound good? Also I'm in.