I think you could please most Pre-One Tam worshippers with one simple change... add a dynamic toggle that increases their overworld difficulty.
I cringe when I see people saying we should go back... Pre-One Tam was okay, but it was segregated and boring. There was no point going back to old zones, ever, you could stomp enemies, but why... no EXP, no materials worthwhile - there was just nothing... if you reached the highest zone possible, you stayed there... being relegated to one zone for the rest of your career was awful.
I personally don't want more difficult overworld - but I do understand that others do - and generally speaking when somebody is praising the Pre-One Tam era, they are mostly referencing they miss the fact of overworld difficulty...
One Tamriel is how this game should have launched, but it can be made better for everybody if this toggle is added. Even if it was rudimentary like skyrim where a multiplier is placed on ingoing and outgoing damage, I think it would make leagues of difference for those who miss the challenge.