[mcdonje]

I like your thinking, but there could be confusion if used imprecisely. Namely, people might think it's a website that isn't broken (this could be seen as a benefit for the playfully opinionated), or a website made primarily with functional languages/programming style.

I suppose you'd have to refer to a site as Functionalist.

[camillomiller]

Well I was thinking Functional Minimalism, but that's already not very minimalistic to have two words to define the category :)