Sometimes it's not the tools, but the setting. This thread was opened by someone that wants to create FR content for the game, and I'd argue that the appeal, initially, for the tools in NWN was also the setting. DOS 2 was a good game, I didn't play it until I learned that Larian was doing this one. Having played it, I can't think of anything I'd like to add to that world. This may be a contributing factor to how few actual campaigns came out of those tools. This IP doesn't have that problem. In fact, the owners of it are still making new stuff, isn't 6th edition in the works currently?
I can't say that it would be great, or that it would be widely used, but I can say that I'd at least "look under the hood" to see what it's about. I like experimenting with tools, when they're available. I'm pretty sure I know a couple of people, at least, that would give this toolset a try, if for no other reason than to try to recreate what they did in NWN in this engine. Is it a gamble? I'm not sure, because I'm not sure what risk there is to including a toolset with the game. If it's like NWN, however, and is just the tools the dev use, it's not like it's going to have a large cost associated with it.
I'm inclined to agree, the interest for creating custom campaigns/adventures may be great enough here simply due to the fact that BG3 is a D&D product. It's also likely people would want to build adventures for other D&D settings, such as Ravenloft, Greyhawk or Dragonlance (or even for Mystara or Birthright).
However, a modkit/toolset also needs to be accessible enough to not scare people away. And there's difficulty... they'd need it to be accessible, yet powerful enough to build some interesting adventures.
