James Britt has this to say on the Rails/Merb merger:
Because Merb was essentially (as best I could tell) a variant of Rails (with ideas from Nitro, Ramaze and other frameworks), it seemed easer for ideas to trickle back and forth between Merb and Rails. Rubyists had more options, and both Merb and Rails could feed off of each other. It seemed a win all around to have them independent.
The consolidation removes this useful competition. This is maybe a plus for folks who prefer Rails, and a gain for people who want to do things the Merb way but can now say they are using Rails. Less useful to people who want to see more distinct options.
That’s exactly what I worry about. In the larger world, though, I don’t expect this to be a huge detriment. The MVC framework market is vast and varied, and there are plenty of good ideas being generated all over the place.