Probably been pitched out there already but an awesome concept I came up with after making a redstone built involving flying machines and other small contraptions and that thing would have made my life so much easier!
A block that when it's powered, it's unmovable and when it is not, it can be pushed or moved on a slime block. Would make elevators much smaller or would bring so much to the redstone community in my opinion!
In terms of pistons this block exist. Unfortunately a piston activated takes 2 blocks, but if that doesn't bother you try using them for stopping your elevator. (I imagine that's what you meant by making elevators easier)