Are there (or will there be) any rules for progressing beyond the level caps in the core book? I suppose that would be considered “epic” level game play
No, there are no rules for progressing beyond the level caps, and there are no plans to support it. 14th level is the absolute maximum level for characters in ACKS. A 14th level character is powerful enough to rule a world-spanning empire!
But honestly, if you want higher level play, there are plenty of resources to figure it out. LL and BECMI will give you the xp charts for example.