The second definition you mention stands out to me as it is one I have been coming across a lot recently (with a reaction of "bzuh?"). I'm not sure how recent it really is, but the shift is interesting.

In my experience, the term "Aca!fan (and it's variations)" has always meant academics who (some of whom, but not all, publish academic work about fandom) are in fandom and both approach fandom with academic tools and modes of discourse, as well as/in addition to nonacademic tools/modes of discourse. I don't think the term inherently refers to only fen who do meta; aca!fen just use a different set of tools, which are neither better nor worse than any other set of tools anyone in fandom might use.