The DM is the difference between D&D being a boardgame and it being a role-playing game. Remove the DM, and I'm just not interested. (I have no problem with them doing D&D boardgames, but as an addition, not a replacement.)
As for Mearls' question: as I said in the other thread on this topic, I prefer minis to be strictly optional. My preferences at the moment lean towards not using them, but my opinion has changed in the past.
I wouldn't play, much less run, 4e without minis. It just loses too much. 3.5e also loses a fair amount without minis, but not quite so much - I do run it without minis. 3.0e was even less minis-reliant. (I can't speak as to Pathfinder.)
I will not buy any 5th Edition that is as minis-reliant as 4e, or even 3.5e. I would play such a system, but won't run it.
As regards the change in the cover rule: 3.5e made two changes. The move from five different levels of cover to just two was a big improvement. However, the "imaginary lines" rules are absolutely horrible - on a par with the grapple rules, IMO. In fact, I never used them, always preferring a handwave. Of course, using a handwave negates any point of having a definitive rule!
(Incidentally, I did a side-by-side comparison of the 3.5e and 4e rules for cover and line of sight, and the "imaginary lines" rules are the same. Awful rules, in both cases.)