I'd like to see some quest challenges that involve less than three party members. You don't really get that experience except in the first couple tutorial maps, and I thought it was pretty interesting having no backup. I've noticed that in some cases the battle is actually a lot easier and more controllable when I only have one character. The enemy takes a turn after each action you make, which means for each party member you'd normally pull out of harm's way, two others are potentially being left vulnerable (especially with minion groups closing in). In this way, having three different targets all together on the board that you're responsible for keeping alive can actually be seen as a disadvantage. What made me really think this would be fun? I've experienced some awesome moments where I was in a large map with some obstacles, two characters were dead, and all that was left was my long range elf wizard. Queue the Benny hill theme song. She ran circles around the enemy, and kited them like a boss, finally accounting for about 3/4 of the total enemy casualties. In other maps, I've built a life-leech Priest who can tank with the best of them. I unleashed him once while ignoring my other characters, and it took about 8 enemies to make him start having to take a step back. This quest mode wouldn't work on many maps, where the enemy size is enormous, space is too enclosed, or there are victory squares that need to be held, but many good maps still stand out as candidates. The goblin maps usually have huge areas you can run amok in, Demon portals can be soloable once you know what to protect yourself from, Everything involving zombies is slow enough for one guy to stay ahead of, and the gnomes/lizardmen are pretty easy to mess with too, because of the way their maps are built. You'd want some pretty specific character classes and gear for challenges like this, and the maps might even need a little bit of altering (is that possible?), but you'd have the benefit of using your best gear condensed onto one or two characters.
Sure, I wouldn't mind a few solo or duo quest challenges. I've played a couple of adventures like that just for fun anyway. I'd generally like to see a bit more variety in the quest challenges. I think it would be pretty rare for a battle to be -easier- with just one character though. If it's a disadvantage to have to pull your characters out of harm's way, you can always choose to simply leave them there to die instead. Leaving your characters to die could be a disadvantage on maps where the enemy controls the victory squares though...