Shadowban users posting obvious spam instead of just banning them. Banning accounts just leads to more spam accounts, and we have no account creation restrictions in place. If they are shadowbanned, they might not create new accounts and they will carry on posting with their shadowbanned spam accounts.
If we are going to implement this, I think it is important to have a clear definition of what we mean by spam. I am not talking about people posting off topic things in the wrong sub, or people making a one off spam post trying to plug their youtube channel on /s/gaming or something, I'm talking about users like mallow and jacknight that are constantly posting stupid shit and not contributing at all.
Reddit's policy on shadowbanning is fucked up, but I think it could clear up any potential spam problems if it was used in the right way.
Edit: If this is implemented, I would suggest not putting this in the TOS or anywhere else. Don't let the shadowbanned spammers know that they have been shadowbanned, or it undermines the effect of shadowbanning.
I agree that shadowbanning is a useful tool to combat spam accounts.
However as seen in the past, it's easily abused and sometimes legit users get caught in the flak.
I think it should be mentioned in the TOS though, few spammers actually read that and it would seem shifty not to address it.