I hope that bethesda makes it so each skill tree caps at... Maybe 130 instead of 100. Even if they add only one perk to each tree. Some ideas for perks.
Archery=double shot (fire two arrows at once) or increased rate of fire.
Enchant=20% bonus to all enchants, or can have any enchant on any item
Lockpick=skeleton key (keep it even after completing thieves guild)
Destruction=2x bonus to any dest spell
Restoration=5 health per sec regen in battle, and 10 our of battle
Smith=either a armor/weapon set greater then dragon, or a bonus like +50% smithing
Sneak=phantom shout, projects a phantom that enemies attack while you sneak around them
One handed=ability to parry and block with one handed weapons if you swing at the right time
Two handed=duel wielding but reduces both weapon damage by 40%
Etc.
I think 130 skill cap would be enough to get the hardcoe players to lvl 100. Also I hope there are quests and enemies that are high lvl only, like dawnguards legendary dragons.