One issue I find is that it will make life harder for GMs.
Currently, if you look at a PCs character sheet and see flash, you have a pretty good idea of what it's going to be used for. If you see Darkness, you have a pretty good idea of what it's going to be used for.
If you unify them, then you have to squint and parse all the conditional limitations and adders and figure out where the player is going with it. I'm not saying that you can't stack modifiers and weird advantages on Flash or Darkness, but they become a little more obvious when you're trying to squeeze some cheese by the GM. With this approach, every usage of the power needs to be scrutinized...