Posted my thoughts on Matrix over on Bluesky in a thread:
https://bsky.app/profile/lina.yt/post/3memjfjwzzs26
https://bsky.app/profile/lina.yt/post/3memmudkm3k26
TL;DR no, it's not going to replace Discord. Matrix is too full of jank due to early poor design decisions to be widely usable by non-technical people.
The Fediverse and Bluesky are different takes on federated Twitter with different pros/cons, and federated Twitter is a much harder problem (because it's "global"), but Matrix is basically just all cons. It's a failed experiment, and you can simply do much better starting over rather than trying to fix it. Just because it's relatively widely used in FOSS spaces doesn't mean it's the way to go. Sunk cost fallacy etc.