This is a great idea.
A few things:
Yeah please no shards, SoG is way to powerful, especially only if one team can use it. Nova and Immo should both be banned, because they can also heavily tip the scales for one group or another. Or you could limit them and make the group who picks them have to skip their next draft pick or two, or make them available to all.
Maybe either limit total number of upgrades or just not have them involved at all. It needs to be one or the other, because some cards lose a lot of value drafting if they stay un-upped or would simply change when they were being drafted.
I feel like everyone has all towers, and drafting pendulums would work.
No trading for at least the first three rounds. I originally thought no immediately towards trading, but you'll have a rather limited amount of decks when drafting if you don't.
Final idea. Maybe present to people what cards are left at their turn for drafting and just have people PM their picks, so at least the first round is secretive and exciting and would limit hate drafting.