There was a talk on exactly this at a FOSDEM years ago, and the verdict was that licence changes were prohibitively difficult if the project was openly developed because you need to acquire permission to change the licence from every contributor. This is why some projects (React for example) require the signing of a contract in advance of any PR merge that transfers the ownership of the contribution to "the project".

So, if Matrix is (a) developed openly, allowing contributions from anyone, and (b) doesn't require the signing of a bullshit CLA, I think it's fine.