It will definitely be controversial, yes. I think even now in its infancy, porn is one of those topics that causes servers to draw lines in terms of federation, so it will definitely intensify if/when Reddit purges porn.

But at the same time, I doubt all instances will clamp down and ban it. It brings a lot of traffic and I'm sure many moderators have strong free speech vallues and will defend it under that banner. It's extra work but some will take it up. There will most definitely be NSFW-dedicated instances in the worst case.