I don't think grognok it's gonna be for public hands or atleast not yet, specially for a game like Destiny. Starcraft has this world map editor but the game mechanics it's totally different from Bungie's grognok. You could expect some sort of map editor, but not now. Maybe in a few years ahead.

Nothing's stopping you from doing that in any other game engine. But it would be fitting if they did a public release of Grognok and allowed level imports like an upgraded forge mode with certified assets. Doubt it'll get an answer (especially so early) but asked about a public release for general use of Grognok in the mailsack this week. I saw them play with the real time lighting slider in the short clip at GDC that in itself would make the engine more desirable to me than Unity. But Unity's build to web player is the primary method I use to show off my games so hopefully Grognok would have a build form that's also easily distributed in a way people aren't completely afraid of downloading and playing.

I think that would be kinda cool. People not only could make their own quests but also things like movies and videos and stuff. I think that would be very cool to see. Personally, im working on my own fan fiction right now, see what happens with it.