1. Use PvP unlocks for PvE heroes. There are 14 heroes in the game and most of us have more than one character. I know most people won't be equipping all heroes on all characters, but it still gets to be quite pricey to equip heroes on each character. Using PvP unlocks for heroes would not only save money, but also space. Want to switch Koss from sword to axe? Just toss the PvP sword and create up a new axe for him. Need different mods on the weapon or shield for a certain area? Just create a new weapon/shield/etc easily and delete it after that area. No wasting inventory for 20 different weapons and shields for different builds.
If this idea is no good then ....
2. Hero inventory. We know heroes and henchies take a share of the gold and loot, so why not enable us to see inventory on heroes, at least. We could sell the hero's loot at the merchant but the money made would stay on the hero and used to buy runes and weapons for the hero. The items (say, if a green dropped for the hero) could be equipped only on that hero. Could help save quite a bit of the money we'll be shelling out for runes and such.
3. Make Sunspear Rank account wide after beating the game once. The grind to make Sunspear ranks would be very tedious after first few characters going through Nightfall. It's already tedious to do once. After one character beats the game it would be nice for Sunspear Rank to be shifted account wide so other characters can avoid the grind.
That's all for now... I'd also love for more quests with skill rewards to be added, but it's probably too late for that.
Nightfall Suggestions
Riesz