I made a similar suggestion to this a while back, because I feared that 'dungeon combat' would become similar to it counterpart in AoW:SM. In the original AoW you could bring only a single party of 8 units to a dungeon battle, and it worked. I usually brought my heroes, and a few regular units for backup, like archers and priests. Battles were also fought inside an actual dungeon. However in the sequels battles were fought on a regular battlefield with some structures added. You could surround the dungeon with an army, and all those units would fight in the battle, making them less challenging and less fun.
Elemental has taken the middle ground between the two games. Battles are fought on a regular battle map, but you can only bring one party. However this party can include squads, effectively making it an army, and removing a lot of the challenge.
The suggestion I made was to introduce a new pack, the adventurer pack, that allows units to participate in dungeon battles. Sovereigns and heroes would automatically have this pack, but it could be added to units in the unit designer. Its costs would prevent you from adding it to every unit, reserving it for the more valuable troops like paladins, rangers, assassins, priests, etc. Drawback being that you would have add this pack to creatures like summons.
Another option could be to only allow 'single' units (so no squads) in dungeon battles. So your heroes, summons and other special creatures could enter dungeons, but you could also bring some regular units like swordmen and archers along for support. I like this idea more, because it could lead to small 'raid parties'. Like in the movie Star Wars Return of the Jedi. The rebels send the heroes to Endor to destroy the shield generator, but they bring a group of commando's with them as well. It would be really cool if there could be a use for these raid parties beyond dungeons, like special missions against your enemies. But that's just me day dreaming I guess 
