You mean the market has changed in that there are finally EMTBs that work as well as normal MTB's at being mountain bikes?
I think its the exact opposite, in that the people i knew with EBikes up until the last few years, where those who either used them to overcome a physical handicap, or where lazy (all though this is relative as how can you truly be lazy if you wan to go out and pedal a bike!)
The last few years has seen an explosion of "core" mountain bikers switching over to EMTBS, because you can get more out of your time on the bike, ride new terrain, and still get the performance on downhills, parks and technical terrain that you have on your normal bike, and basically have a load of fun
As for fitness (something i don't ride a bike for, but benefit from from riding the bike) i find that ebikes encourage you to thrash out a ride, rather than having to stop to get your breath back, the assistance enables you to maintain operating at your peak performance, not compensate for a lack of it - i have lost more weight since owning an e-bike, simply because i ride it more than i ever did my old bike, and push myself harder on it.
Also a serious EMTB is a serious MTB, if you don't know what you are doing, and don't have the skills to ride the terrain, you are going to get in trouble pretty quickly - if you ride the terrain these bikes are designed for and don't have the fitness or skills, your on a one way trip to a & e