Personally I am not a fan of games that move the goal posts regularly...but Niantic have shown that this is what they call 'developing the game'.
I am not sure it will happen any time soon...but I suspect it will happen eventually.
For the record...no one pushed anyone to get to lvl40 quickly, it was their choice, so if they feel demotivated because they don't get levels anymore, then that is on them (unless they got lvl40 with pure grind and very few empty xp evolve sessions...then much respect).
Personally, I have intentionally not done many 'evolve' session for empty XP, as I intend on playing for a while yet, and I know that lvl40 will come naturally without me needing to risk my future motivation.
EDIT Why the downvote for my opninion? Feel free to discuss it.
...or is this just one of my regular readers letting me know you have seen my post?