WOW! Didn't see that one coming. ALL THE POINTS!
I couldn't really get on board with Snoke. He sort of struck me as diet Palpatine so much that I really didn't mind him getting punked. Maybe my feeling on that would have been different if like you say they ever explained what his actual deal was supposed to be. Now there's a hole where it seems like a villain for the story should be.
The entire canon has rubbed me as "diet" with tons of artificial fillers. The bad guys are just big meanies, the heroes are nauseating clichés, and rest is just mind numbing throwbacks and recycled designs. You ever get the thought they were hoping we wouldn't notice that they really had nothing but a lame social agenda?
But I don't know that I want The Emperor's death in ROTJ retconned to fill it.
Think of it along the lines of Sauron's "death". Everyone thought he was gone for thousands of years, but he was really biding his time and gathering his forces. I can totally see Sidious being patient enough (#sithlife) to do this same thing. Snoke may have been significant opposition enough to prevent his return.