I'd really like to see something like this on Mastodon, on Home feed and other main feeds. We should be able to know what the replies are about without having to open the whole thread.
Right now the replies don't mean anything unless I open them. Unmaintained Mastodon client Halcyon manages to do this, so it can be done in core as well. I once tried it via JS but my skills are not enough for it to be reliable enough.
