It's been said before that with level 100 being a very iconic max level for the series, that after DT we will likely stay at level 100 and explore alternative levels of progression. I don't foresee a level squish. While it's entirely possible that Yoshi P could change his mind on that topic, I think just not increasing the level cap at all and doing something else is the better long-term solution anyway.
I've been thinking some interpretation of the Sphere Grid could be really interesting.