I voted for no limits ...
In my eyes, that is pure Quality of Life upgrade ... so you dont need to travel through dead land back to Waypoint, to port back to Emeral Grove, to sell your loot, after you kill everything that was in that zone ... wich is main reason i ever fast travel.
But i also voted for Limit by zones, bcs i believe that is exactly what it is right now ...
Maybe, just maybe i would add few more "danger zones" as Hag's Lair is right now ... but only where and WHEN it makes sense ...
you are stuck in cave, surrounded by Gnolls? > Danger zone ...
you are inside spider-monsters ifested vell?> Danger zone ...
you are inside Goblin Camp, where you can eat, drink, trade and talk with everyone you see, no matter they are discusting canibalistic monsters? > NOT Danger zone, until you kill Ragzlin and they all turn hostile > then Danger Zone.

Also, yesterday i just started to replay Dragon Age: Origins ... and that game perfectly reminded me everything i hate about random encounters.

I had to travel from point A to point B 7 times to trigger sidequest, that is hidden in random encounter. (What kind of idiot even come with such idea?)
I rushed from point A to point B, bcs i had important quest ... nah, too bad, here is huge army od Dark Spawn, you just "randomly met on the road". Great! -_-
I rushed back, poof yet another encounter ... this time just vendor, but having nothing interesting, so in fact just delay from what i really wanted to do.
Yeah i know they arent exactly "random" since every time you travel in that game you tigger some (or it seems like it at least) ... but still, it was NOT good experience in any way.