For an indie game developer, gaining some of the ‘community building’ tools of Reactor for a game could be quite handy. Not to mention the ability to easily hook into various achievements and so on.
OTOH, this would only be available through the one distribution channel, and doesn’t work for Steam, direct sales, etc.
Worth the while, or wait and see?
I haven’t really looked into it to be honest, but I’m very wary of designing my games to be locked into a system owned by someone else. If I really wanted to do that, I could just go work for a developer 
Impusle Reactor is certainly not locked to impulse. The game needs to be available on impulse but can be sold in any other way too.
I only wonder if its compatible with the steam overlay. Would two Overlays work in one game?
Indeed, it does seem it has been specifically designed not to be locked in. They basically developed this to stop developers using steamworks, and thus stop devs getting locked into steam.
The thing is, these systems are designed around DRM, chat and matchmaking, and none of those 3 are needed for GSB