We had a great discussion at the MediaWiki dev summit just now on
service-oriented architecture and future plans in that direction... as
always the community seems a bit split on the subject.
Breaking things out to separate services can indeed make setup and
maintenance more complex... pro-services/pro-VM/pro-hosting folks like me
tend to say "hey that can be automated!" (and MediaWiki-Vagrant shows a lot
of awesomeness to start, though it's very developer-focused).
One thing that comes to mind though is something Gabriel mentioned about
wanting stateless services for things like image manipulation and citation
parsing and whatnot -- in principle many services like this could be opened
up to public use.
For instance, a random MediaWiki instance could use a Wikimedia-hosted
image scaler or graph rasterizer.
Usage limits and API keys could be introduced if we're worried about
overloading.
Whether this can apply also to things like Parsoid might be tricky --
that's the biggest Scary Thing since core editing with VE/Flow is going to
depend on it.
Anyway, just thoughts. :)
-- brion