You seem to be saying both that there is too much work, so there won't be time for mediawiki development, and that there is too little work so they'll be twiddling their thumbs. Which is it?
Both.
MW development is a whole job in itself. From experience; it's hard to work meaningfully on a major project (such as that) whilst also doing smaller bits of work (like outreach, sysadmin, smaller development tasks). Especially if you are managing yourself.
(I'd point out that the WMF model is worth examining; where they hire technically inclined project leads/managers, and the grunt development work is done by specifically hired devs, contractors and volunteers.).
Tom