For example a political post in s/nopoliticshere can be moved to s/politics by the mod of s/nopoliticshere.
This accomplishes several crucial things:
1) Prevents censorship (and drama) by not removing the content. The same thread exists, just in a different sub and still shows in s/all.
2) Grows niche subs. Maybe nobody goes to s/politicalmemes but they will if they like the content that gets moved there from s/funny.
3) Keeps content relevant to the sub in two ways - subs get relevant content imported from other subs, irrelevant content gets removed from the other sub.
Discussing this in IRC the main concern was abuse. A mod can dump a bunch of posts into other subs. A potential safeguard would be for mods to disallow transferred content from other subs. When another mod tries to transfer content there they get an error and have to choose a different sub. And of course the receiving sub can just transfer the thread again if they wish if they allow transferred content.
There still has to be a full deletion option for illegal content, but I think those instances are few and can be handled through an admin reporting system.
I'm sure that's where a LOT of content will wind up. Which is fine. There could also be a dedicated spam sub like s/spam for that content as well. But if you don't allow mods to transfer to the niche subs I think you miss out on a lot of the benefit for this feature.