First I want to say, the job on mage passive is already great.
I meanly play melee pure thunder spellblade (full melee manastrike other active are for protection) with passive that augment attck speed. i used the ligthnening spell manastorm and shock from manastrike with passive that augment spell damage with melee attack. Other passive are the one that augment max mana and ward creation/retention.
I love passive that cast spell like ligtening rain.
For spellblade, passives that play on chaining melee and spell are good mecanisn.
There is a lot to do with ailment. We can do something with applying the three elemental ailment (chill, shock and ignite) on same monster for multi element build.
Or just with two element like chance of special effect on chilled monster when attacking with thunder.
I don’t really like on kill effect, but I understand that it is aninteresting mecanism.
Perhaps some passive that give bonus with ward value (like the unique bee sword).
I really like the idea of double cast. Free cast is great too but I will not use it personnaly.
For runemaster, the same as ailment but for the caster. A little like rune word.
That it if rune are like buff on the ground given by others passives or tree on skill… That could be great
Sorry for my english.
Hoping that help.