I do not understand why 3CX has thus far not answered the question about whether this feature will return. I can only assume that it isn't an priority for them at this time. I hope that I'll be pleasantly surprised and that it will return in some future update. However, with our new school year having just started, I couldn't wait and had to make adjustments to deal with the lost functionality.
@Igray and anyone else dealing with this issue :
I understand your concerns about custom phone templates, but if it's any consolation, we've been using them for the several years that we've been using 3CX. There are certain multicast paging capabilities, BLF programming, and other functionality that we require that have never been configurable through the 3CX interface, and with as many phones as we have it's not practical to program each phone individually. When we began with 3CX there was no "Enable Multicast Paging Ring Group provisioning" option in the interface, so we had to have five separate custom templates - one for each zone with its own paging requirements. Several years later we were thrilled when the option was introduced as it allowed us to consolidate our five templates into one. Now that the option has been removed in v20, we have had to return to five separate templates.
As far as manually configuring paging zones on the phones themselves, I could be wrong, but I think this could work, perhaps depending on your phones. With respect to support for custom templates, where this could come into play is that if you're having problems and need support from 3CX, you would need to temporarily configure the phone(s) with a standard template before they would assist. This has not been an issue for us yet.
I hope this helps some people. It seems to me that somewhere in the forums is a wish list or feature request area, but I'm not sure where.