There is no easy way currently for supporting the development of MediaWiki features / extensions important for one's work. Integrating some kind of crowdfunding functionality into MediaWiki.org could enable more community-funded work.
Payment processing is scary and expecting a Wikimedia entity to do that is probably not feasible; also, building a decent crowdfunding site is hard. Fortunately, several opensource-focused crowdfunding sites exist (e.g. Liberapay, Open Collective, Bountysource, FreedomSponsors) and might be easily integrated - the functionality would not be terribly different from embedding an external RSS feed.