One thing I assume will be a sizable annoyance: is that E2EE won't be possible across the bridge, unless both sides adopt a mutual E2EE protocol. Thus it might be the first case to see a push for experimental implementation of MLS (from MIMI), or otherwise bring some Olm/Megolm compatibility to XMPP, or OMEMO compatibility to Matrix, as I don't know if those can be 1:1 translated back-and-forth. Or just less-sophisticated things like PGP over instant messaging (like PGP over XMPP as transparently facilitated by plugins).
They're both key ratcheting systems, I just don't know how much Olm/Megolm differs from OMEMO.
But at least it bridges the communication gap to be able to start reaching people on another sizable federated instant messaging network.