Would these changes make Spell Vamp a stat that can have a major item?

Worth a look into.

Would also be interesting to see how those numbers would interact with lifesteal.

Seems like Octarine core from Dota2

Except that Octarine core unlike old Wota costs 5900 gold and not 2000 gold My point is that Riot removed Spellvamp because it made Vladimir's laning phase unimbalanced and other manaless mages like kennen/rumble

Vlad ruined spell vamp, and now with how akali's passive works she would probably break it as well. The problem with spell vamp is that mages get big heals from spell rotations while ADCs are suppose to get only small heals from each aa but those heals add up if they are allowed to keep attacking.