Matrix?! As someone who runs is own Matrix homeserver, oh, man, no way. Matrix is super fiddly, unreliable, and user-unfriendly (and I say this as someone who has at times agreed that Signal can be user-unfriendly).

Matrix also is just not particularly private. Servers control and know far too much about users, and pretty much no mainstream client enables E2E encryption by default. Matrix is an impressive piece of technology, but it has a long way to go before it's as usable for an average mobile phone user as Signal is.