Can you explain how IIgs emulation doesn't need a ROM? Dragon wars is a GS/OS application, so indeed needs bits of the operating system as well to function.
Having played this on the Apple II, IIgs, Amiga, and MS DOS, I would say the IIgs and Amiga are both my preferred versions. The Amiga has better sound while the IIgs version is a bit less clunky in the UI.
Given the way that Bard's Tale 1/2/3 are packaged, it seems pretty certain that inXile cut a deal with Apple, or are at least taking on the legal risks. It's unclear if the current Dragon Wars rights holders (current Interplay) have access to that, or are motivated to jump through the hoops.
Personally I'd be overjoyed if GoG could acquire a licensing arrangement with Apple to enable selling IIgs games in general. MESS is pretty high quality and seems to be moving towards a proper open source license that would enable this type of commercialization.
I'm making an updated version called "Dragon Wars: Remastered" where the code came from the unreleased Windows version, art is from the IIgs, the music and sound is redone by 8 Bit Weapon and background art redrawn by Jennell Jaquays. It will be a native app for Mac, Linux and Windows.
If I can cut a deal, I'll do the same for the Bard's Tale Trilogy.