Vidiot: Decrease.
I agree. If they go fully mainstream, they become just another Christian church. But that requires a long list of changes. These changes will alienate the old-school hardcore JWs, but will do nothing to make the religion more attractive to potential recruits.
Allowing birthday and holiday celebrations? Congrats, you are starting to catch up. Do away with shunning and the blood policy? Again, lots of other Christian churches don't have this issue, plus it will generate a LOT of criticism from loyal JWs who suffered under those policies. Their view of the afterlife for sinners is better than the concept of eternal suffering, so I guess that's one possible point in their favor (even if it's not unique). Goodbye, governing body? Goodbye, book publishing? I don't think you'd have anything left, if that went away...
I don't think they can go completely mainstream without shutting down. I'm more interested in how far they will go, and how their decisions will affect the numbers along the way.