I also find the concept of humans becoming energy creatures ridiculous, but at that point its just something I laugh at. The human encounter suit was just stupid. Every older race doesn't need to evolve into pure energy, but even if they did I don't think 1,000,000 years would be quite enough time for humans to become energy. Still, the telepath war stuff is the biggest fear this episode and the first ep of Season 5 put into me for the immediate future of the show. I really hope we can get through the season without it, but I wouldn't even bet a penny on that.
I think it's less evolution and more high-end cybernetics. One of the RPGs explains that the vorlons basically just shoved copies of their mindstates into engineered space-time defects, making them sort of like one of Arthur C. Clark's precursor races. At some point you start replacing the meat and bone with metal and plastic, because the metal works better. Then at some point you start replacing the metal with engineered folds in space-time, because engineered folds in spce-time are more durable than metal.
And, you must remember, that humans, minbari, and many other races were specifically engineered by the vorlons with this outcome in mind. They weren't just creating telepaths, they were playing a very long game.