How about adding some side quests for each of the main characters perhaps a battle where you would only use that characters specific units.
the rewards should be a weapon and armor for use only by that character and the extreme battle could give that character a unique ability the rest of their units wouldn’t have.
Sidequests
good idea. Maybe be able to complete a quest and receive a unit for doing so. IE: Protect the Village/town and one of the soldiers/archer decided to join your part instead of using up your scrap
Even if they didn’t want to go as in depth as to creating a whole new stage they could just possibly even make certain conditions on a level, or certain things you have to accomplish by the end of the level.
We actually are planning on adding a few sidequests to the game in the “Big Update” that’s coming in 6 weeks or so. We’re still debating exactly how to do it, but you’ll at least have some unusual situations to play and some branching options here and there. The game will still be mostly linear (we’re talking probably 4 - 6 side missions, not an entire expansion pack), but hopefully it’ll add some more variety and interest.
— Begin quote from "Anthony"
We actually are planning on adding a few sidequests to the game in the “Big Update” that’s coming in 6 weeks or so. We’re still debating exactly how to do it, but you’ll at least have some unusual situations to play and some branching options here and there. The game will still be mostly linear (we’re talking probably 4 - 6 side missions, not an entire expansion pack), but hopefully it’ll add some more variety and interest.
— End quote
sounds good is there any possibility those side quests will revolve around the main characters then?
Almost certainly, but that’s mostly up to James.
niru should also have something to equip to separate her from the other dragons don’t know would it should be but the storyline characters should be special
can’t wait to see the newgame + sidequests
Lans, the 4-6 new sidequests would each reward a new book for Azra, right? It’s a reasonal assumption but maybe it’s going to award some special weaponry/armors?
The side quests are only NG+, right?
yes NG+ only
Haven’t decided exactly what the sidequest rewards are going to be just yet, but books seem like a pretty reasonable option 
And yeah, Sidequests are NG+ only.
— Begin quote from "larsiusprime"
Haven’t decided exactly what the sidequest rewards are going to be just yet
— End quote
Bonus movies would be pretty awesome. The events leading up to Azra being thrown into the pit as one, for example.
As would be a permanent to bonus to individual unit types. Say, all archers gain +1 to maximum range. Little things that make getting higher and higher waves on Endless maps possible.
Or bonus unlockables from the main menu. Concept art, notes from the developers, an in-game music selection.
I’m still hoping for storyline character specific weapons and skills
Yeah,there’s a lot of options here.
- Unlocks a way to upgrade some of your Named Equipment. (Swords can now be upgraded by doing insert mechanic here!)
- Simply shows you additional cutscenes - a story reward. I’d be perfectly okay with this; some might feel let down at “doing all that work” and not getting a material reward of some sort.
- Rewards you with rare equipment (personally I lean towards seeing it give you more Books for Azra).
- As was said, some sort of passive bonus to a unit type (or types). Personally I’d like to see this one if each sidequest featured one of the Hero characters, and then gave said statistical reward to the class that Hero represents.
I’m sure there’s other options, but this is all I’ve got at the moment. In any case, pretty intriguing stuff to speculate about.