quick swap
A skill that reduces the equip cost would also be very appealing for the inquisitor class (dual wand users), because you can better adjust to the elemental resistances of your opponents.
melee weapons with ranged damage
I could see weapons that unlock some basic magic skills like Flare or make Staff of Magus compatible with all Tenebrium weapons.
Currently getting a few levels in another "class" is encouraged by the low amount of skill points that are required to learn their basic skills. With their 100% success chance I am putting Teleport + Thunder Jump on all my chars and Melee Power Stance + Helping Hands on the Mages, but the elemental damage / status effect success rate of other magic spells just suffers too much to be used by low int chars.