Will we see an open world / adventure style mod with Forgotten Gods?

Short answer is no. The new Merit tokens will allow you to skip up to another difficulty so you could jump between Normal, Elite and Ultimate if you want to, but that’s it. You still start in DC once you change the difficulty setting in the main character menu. Skipping up to Ultimate will mean that all riftgates and shrines will be enabled on lower difficulties.

And skipping difficulties with a low level character will bring it’s own hazards. From the 7th December stream:

"anathema2741 : how is the level scaling on ultimate at level 2?

Well, let’s take a look. Now I will warn you that anyone who’s going to play like this? It’s going to be hard. I would describe this as almost playing on players 8 in Diablo 2 back in the old days, but you’ll notice these enemies are actually scaled to my level. We’ve gone ahead and through Elite and Ultimate difficulties and updated these guys so they scale from one all the way up to max level. And yes, they hurt. They give a lot more XP, but they hurt. You’re going to get all the attribute and skill points like I said and you’re going to need them because this stuff is way harder than what you’re used to. I will point out, if you look at my resistances, they are in fact altered by the difficulty scaling."

http://www.grimdawn.com/forums/showthread.php?t=77182

Plus Zantai already replied to this in your previous thread on the subject.