As a federated protocol, is there anything at all in the spec that would discourage someone from piggy-backing on the federation to acquire initial users, goodwill and a head-start on features, and then locking users in once they've gained enough momentum by making proprietary modifications?
You know, the same tactic countless companies have pulled with XMPP?
I've been eyeing matrix.org for quite a while now, but it seems to still lack a "killer" client app. One that can at least match the features, polish, stability, usability and platform ubiquity of existing proprietary messaging apps, an app that can help matrix.org grow user mindshare and keep it.
The open source community just doesn't seem to do a very good job of churning out these kinds of consumer-oriented apps. And if some company ends up building such a "killer" app for matrix.org and gains momentum, they'd have some very sweet incentives to lock in their userbase.