Throwing something into the Insert/Replace/Append arena:

IWBNI there were a top-level "Browse playlist" menu, that looked just like Playlists, but instead of replacing the current running-order, selecting a tune (or the "whole playlist" arrow icon) would bring up the Insert/Replace/Append action menu, positioned at the last one that was used. And selecting from that menu leaves you where you were in the playlist tree, ready to make your next selection. This would allow users to quickly build up custom running orders.

Three little differences (not needing a long press to get the action menu, having previous action ready to repeat, and not leaving your current menu position) would make a lot of difference to this activity.

Alternative implementation: make it a config.ini option that that Playlist menu could work in this manner instead of the current way.