[JulienSchmidt]

I really appreciate your efforts. One of the most frustrating things to encounter as a student doing research is a pay-wall.

Regardless if such kind of search was available before or not, many people, like the author of the linked article, will encounter this pay-wall during their research. I think you could benefit, and especially grow, a lot if academia.edu becomes a place where students actually start their research instead of landing there through an external search engine.

In 2017 fulltext search should be considered a basic feature, which according to your business model should be free. Even the online library of my university offers it, even though on a much smaller data set.

If it is true that other premium features are more heavily used than "advanced" search, then you still have enough reasons to legitimate your premium accounts without it.

I think you could find other ways to generate income and become sustainable. For academia.edu it might be premium accounts offering additional services and maybe sponsored content like placed search results, job offers etc. Use the information you generate (but please don't just sell it to a 3rd party).