Why should I take spellthiefs after these changes?
Why would you remove the 25% mana regen from spellthiefs edge? I get that it provides on-hit damage and AP, but what good is that if you can't use your spells? Before you say that 25% mana regen is little, you would really need them on the likes of Sona, Karma, Nami which have some of the highest base mana regen of the game and get a lot of value out of this 25% mana regen. If this goes through, it will probably get very boring down in bot lane with all enchanter supports going coin for the mana sustain, and again the tank engage supports trying to kill the passively playing coin supports.
I can kind of live with the other changes, but please bring back the mana regen on spellthiefs.