It doesn't solve the problem initially presented. But the solution is still useful because I still need to delete many files through Rockbox. This is not a issue with any other DAP's original firmware, so I'm surprised that Rockbox can't handle such a simple use case.
Many OFs don't allow you to delete files. Many others force the use of a database (look how long the e200 requires you to wait on bootup for it to scan and create its database before you can use it if it's in MSC mode). Many other take quite a while to recreate the playlist.
Simply put, yes, some other OFs may avoid this issue, but at other various costs of their own. Meanwhile, it's trivial for you to avoid this issue by either bookmarking or re-selecting the file to resume from, while the advantages of the way things are done exist for people who don't delete these files.
Honestly, if you
need to delete many files through Rockbox while still listening to files in their folder, maybe you should examine your use habits. Perhaps try putting songs you know you like in a separate folder from the songs you're considering deleting in the first place.
Or the most obvious and simple solution - instead of simply playing a file in the folder, quickly create a playlist of it through the context menu and play that. This takes a few seconds more, but will not suffer the problem you're describing.
Or use the database.
Basically, there's a list of solutions to your problem, so I don't see why you're focusing on the one solution that requires additional work be done, and takes certain existing advantages away from people who don't for whatever reason apparently frequently find themselves deleting files.