There should be an interface that allows other parsers to be plugged into the software e.g. Parsoid (implementation of the same language in a different way) or for 3rd parties markdown or some other language (implementing the interface of the parser but providing a completely different language - seems to have been attempted in some form before)
Concretely, we'll need to pave a path to allow mobile web to switch to Parsoid as its main parser engine to serve VisualEditor better and allow us to optimise better for slower connections by having more control and semantic meaning behind content. Given the current state of Parsoid mobile switching to it would not have any known negative impacts to user experience (for instance video/audio not supported by Parsoid but already terrible support on mobile web).
Long term, we'll probably want to switch Vector and our other skins to Parsoid too when Parsoid is more complete. Mobile can help drive this.
Output: We'll need to setup an RFC for this.