Unlike some people, I was fine with the Darklands-spreading PE mechanic since there are rituals to clean it up.
This is not the case for Dreadland Spread. Once a chunk is Dreadlands, it's ruined forever. All you can do is do the purge ritual, but Purged Lands are just as bad. So an option disable the spread of this would be very helpful.

Alternatively, add a way to restore Dreadlands chunks.

I second this. Its extremely annoying to deal with and im about ready to just uninstall the mod. Apparently its a wide spread annoyance.

How exactly does the Dreadland spread work? I've heard of it in the patchlog but I yet to see it. I am going to make an floating island portal to contain it if it's anything like Terraria Crimson spread.

Agreed, it's really annoying. It's only happening on one world for some reason but either way it's annoying.