I think my ideal 6E would be something in between 2014 5e and AD&D. The somewhat streamlined core systems and middle-ground complexity "character builds" of 5e (by middle ground, I mean between TSR era and my first and second hand understanding of 3e/4e/The Pathfinders), combined with the larger subsystem/procedural scope, (optional) turning up of the simulationist dial, openness, flavour, and particularly the higher-risk higher-reward gameplay style of AD&D. I want some well tested dungeoneering/exploration/large scale combat procedures for those that partake, reams of random tables, devilish puzzles and traps galore, high impact and high risk magic items.
This would be sort of backtracking from the changes from 2014 -> 2024 5e. (If you will permit some mild negativity) I would want to leave the Pathfinder-2eifying to Paizo. I don't want a bunch more character abilities, I want resource management at a strategic level above the encounter, I want balance of high rewards through high risk rather than muted numerical modifiers, I want effects with game-impacting flavor, I certainly want the old Command back.
A new edition of D&D does need to be something of a compromise/jack of all trades between different styles (for rules and aesthetics), something that can be modified to table tastes, and can possibly serve as a funnel to more specific TTRPGS. I suppose I am proposing a different compromise (maybe less popular, but sometimes I wonder!) than it seems like things are heading based on the 2014->2024 trajectory, but this is how I'd do things.