I agree that a Quick Edit feature in a slightly expanded view would be highly useful on mobile. I've added an idea with BPM/Key/Add to playlist as the other optional quick edits.

https://support.mixo.dj/t/2241-quick-edit-feature

There is a select tool in the top right for adding 1 or more tracks to a playlist so it may be redundant to add another way of doing this for that one specifically.