I honestly don't see how it's "so hard" or "too vague", this theme is actually quite good Imo, but everyone has different opinions.
Basically, Inconvenient Superpowers is, well, Superpowers that are Inconvenient. It's pretty much the least vague Game Jam theme I've ever seen, but that may just be me.
Edit: dang that was kinda passive aggressive, sorry.