is it available now? it would be a very helpful feature

Yes, very necessary! Especially pagination, so relations with thousands of child entries can be loaded quickly in the Content Manager.

And when doing that: built-in filters on the relation would be great too, in order to make it possible to actually meaningfully edit them if they're thousands.

Yes please!

Is there an RFC for this? It would be great to provide the ability to filter the options, perhaps based on other field values or by collection type.

Oh yeah! This is great. Never understood why can't relations be freely moved around and have to be crammed to the right-hand side panel

This would be great, i have a single type with relation and think it would look nicer on the left

This feature could be useful to improve the visibility and possibly propose a display of the relations in tag mode.