Possibly controversial opinion:

Some instances may adopt bizarre policies, but so long as they're not bothering you or anyone else I think they should just be left to it. There isn't really a reason to block them unless they're causing aggravation or hosting illegal stuff.

I expect the fediverse will continue to get more popular in 2018, and I also expect that some instances will try to add advertising or sponsorship, just because that's conventional (maybe some are doing this already). If that happens then so long as spam isn't getting into my timeline I won't need to block them.