This is what I think a lot of us wanted for years. Them to simply get the all the past dungeons and just apply a simple buff/debuff effect like Deep Dungeons do, to increase your incoming damage, increase boss HP and outgoing damage, reduce telegraphs or speed their casts up as you said, and adding an enrage cast. Others wanted them to simply apply a random effects buff to make each playthrough different, like what deep dungeons do. Really the exact technology they use in deep dungeons to buff/debuff you and enemies would be fine and achieve most of this.

Their answer to all that was to make criterion dungeons. They seem unwilling to revisit old ones, despite that it would instantly give people over 100 dungeons' worth of challenges.