What I don't understand is the O'Briens. Earth? How much botany can there be left to discover on Earth? And Miles would want to be fixing things. He was happier on DS9 where none of the Cardassian and Federation technology saw eye to eye then he was on the Enterprise, just doing preventative maintenance according to schedule. And I don't really see him as the teaching type, not for a class.
Well in "Family" they were talking about raising a new continent. Plus you can still study alien plants on Earth. I assume all sorts of alien plants and trees have been recreated on Earth soil and maybe even some plant hybrids.