If we want people to use the awesome API we have made, the rester needs to be easily installed. If you don't have 3.6, its not easy to install.
I get that the extra requirements are for the non-rester parts of the code. But if they make installing the feature that the most people will be interested in (likely the rester to access the API) more difficult, then they are not serving much good here. Maybe we could relocate them to another package, or have mat scholar's rester be its own package, matscholar-rest or something like that, with a minimal set of requirements and which we can easily put on pypi.