2010/9/22 Trevor Parscal tparscal@wikimedia.org:
Modular feature development being unique to extensions points out a significant flaw in the design of MediaWiki core. There's no reason we can't convert existing core features to discreet components, much like how extensions are written, while leaving them in stock MediaWiki. This sort of design would also make light work of adding extensions to core.
Making MediaWiki more modular won't magically make it possible (or even desirable) to write any old feature as an extension. Some things will still have to go in core and some things we'll simply /want/ to put in core because making them extensions would be ridiculous for some reason. It's true that more modularity will lower the difference in awkwardness between doing certain things as extensions vs. in core (and is generally desirable), but I also don't see how it would make (much) lighter work of adding extensions to core: most extensions should either be easy to add to core (Vector and WikiEditor for instance, any special page extension) or cause some bumps because they were written in an awkward way to begin with, probably because it'd have been better to put them in core.
Roan Kattouw (Catrope)