I've just been checking out lemmy web client called tesseract and it has a client-side group function. This is not a multireddit function, but just a way to organize your subscriptions (basically like adding tags to communities). But i was thinking... what if i was looking at my subscribed feed, and clicked on one of my "group" names... and the client then filtered my subscribed feed to only show posts from communities in that group? That would be multireddit-like behaviour, and still use back-end for sorting/merging and whatnot. Not as efficient as server-side multireddits, but it might be a possible workable hack if one didn't want to wait for lemmy to add the functionality on the server.