@SteveW (sorry; "reply" not available):

Literally, WP isn't topped out; it's gained another 1.5% or so of overall market share this year. But given its prior year-over-year growth, you gotta be concerned (and ... 50% ... ? Sorry, but never gonna happen)

I also agree that MaTT looking outward is a good thing, and to his credit was talking about that early this year as well, although the context at the time was that "the community needs to look outward", not that Automattic did.

My issue with the decisions being made and reason for concern about the continued growth of the platform transcends all of that. REST makes WP itself all but obsolete (think about it; WP is really just a backend to PHP and MySQL, and REST reduces "WP" to nothing more than a database schema).

OTOH: Calypso is Automattic creating a REST-driven front end to that schema, so if the world flocks to it then with any luck the commercially-driven WP entity manages to maintain some control. But that's at the expense of the community, isn't it? It drives people to the hosted platform.

I have thoughts about what would have been a better plan, but they'd only sound self-serving/sour-grapes-ish, and I'm not interested in taking that posture. WP is what it is, and as long as easily-accessible host-it-yourself options remain available and develop without getting forked off the commercial version of WP, WP will continue to hold a dominant position for quite a while.