A unique thing about guildhests is that they utilized the area map as the arena.

This could have been an opportunity for wide area strategic gameplay.

The current maximum level guildhest is lvl 40. That basically means the content has been abandoned for future expansions.

Perhaps what I'm imagining is like a hermit crab crawling into the shell of something else.

Guildhests, or something like it, could have been like PvP, but cooperative against NPC enemies.

Consider a mode of gameplay where there are endless waves of increasingly buffed enemies that don't stop until objectives are accomplished.

A defense mode and a survival mode would be an example. Seeing how far one could get could really push gameplay.

A siege mode could be similar but have another nuance to it.

A capture mode involving breaching locations to take them over, using that as a foothold to breach other locations.

A time attack mode, where an objective must be accomplished in a short amount of time.

A race mode, where you have to keep moving or suffer environmental hazards, or an enemy has to be repeatedly killed in order to keep it from moving faster than you.

Not only would this train the skills needed to do harder content, it would be fun in its own right.