My understanding from superficial observation is that they are trying to fix the (perceived) mess that was R6RS, and thus unify the community.

That would be the case. Some people were unhappy with R6RS not keeping Scheme a minimal language anymore.

Now they're making one "small" Scheme and one "big" Scheme. That's a good thing because they can actively decide what to put in the big version (full numeric tower, e.g.) and what to put in the small language (e.g. a standardized module system).