Remove the VIP level limit for hiring heroes from Special War Powers. This is alredy no serious. The characters from there are not so strong. Give them access to VIP 0 people.
I feel like all the opinions shared so far are pretty good. I think a new level cap would be nice. On top of that i think a new way to farms stones for f2p players and have it be wheel friendly. I like the Soul King addition (I recently started replay on server 639 and thing popped up and i was excited.)
I believe new taverns partners for f2p would be awesome. Or throw old partners in tavern for Red Reishi. Like TDI would be 4k red reishi or somthing like that. I think giving people access to old partners in f2p would breathe some life into the gamr.
I also think a new pvp mode would be excellent. Somewhere besides CSB, because people block in CSB by joining late so they can get free inferno stones kinda cucks f2p players from Muken, etc.