The reply issue is pretty hard to solve, since sometimes the extra text is useful, sometimes it isn't. Perhaps if there has been N minutes or X lines of chat since the message being replied to, then include the extra text, otherwise don't. The template should be changed to something like this though:

    <foo[m]> bar: re "hello about something longis...", hello!
    <foo[m]> bar: re "short hello", hello!

Those are the main ones, a few more:

Image uploads could probably just post a link to the image instead using /me uploaded an image: foo.png (123KiB) < https://matrix.org/_matrix/media/r0/download/matrix.org/....... >

Directing a message at a specific person on the channel sometimes posts their full Matrix URL on the IRC side, rather than just using their IRC nick:

    <foo[m]> [bar](https://matrix.to/#/@bar:matrix.org): hello

Directing a message at a specific person on the channel sometimes posts their full name on the IRC side, rather than using their IRC nick:

    <foo[m]> Bar Baz: hello

Matrix <> IRC splits seem to occur more often than IRC netsplits.