I may add a "matrix plugin" [2] if I feel like it someday, but probably after I implement group chat support. Then you'll be able to use XMPP<->Matrix<->some-other-thing for extra over-engineering points. ;)
I prefer XMPP because it's lighter on resources, server-wise at least, and it's managed through a democratic process, which has it upsides and downsides. As someone I like said "democracy is boring, dictatorship works faster".
[1] https://github.com/mautrix/facebook
To be fair, one of the reason I use XMPP and not matrix is that I didn't hear about matrix until after I managed to set up my own server and get some of my entourage to use it too, about 5 years ago or so. Interoperability is the important part anyway, and I'll work on slidge-matrix when I fix/improve some stuff in the existing core/plugins.
Based on their Github profiles, 7 are affiliated with Element (either employee or CEO), 1 isn't