Hello jclarkw2. An interesting question. We do promote our IMAP service in preference to POP for a variety of reasons mentioned at the link below:
https://help.runbox.com/imap/
That said, we have no plans to drop POP, and when we moved to our current POP service we did ensure that we kept all the same functionality as with the previous service including the
POP from Folder feature.
More recently we included POP in our upgrades to ensure that only secure connections could be made to our servers.
I think the above shows a commitment to keep POP even though it is declining in popularity in general. While we can't offer guarantees, we can say that we have no current plans to drop POP. I hope that helps.