I'd assume that it doesn't take much more than changing the device ID of a 980 EFI to make it work on a 980 Ti (at least that's what you have to do with AMD cards, don't have much experience with Nvidia). So the question is whether the eBay guys have built their EFI from the scratch or just reverse engineered / modified MVC efforts.
It's quite funny to read these "IP conflict" threads here and at netkas forum. As far as I know, MVC always includes some 'signature' in his EFIs, e.g. some technically unneccessary modifications, to convict thiefs when they start selling/publishing his EFIs, and he has been able to do so in all conflicts I've seen.
Besides that, none of the eBay guys have ever contributed any improvements to the community nor shared any of their wisdom (in contrast to MVC and netkas). They both provide quite detailed explainations how they figured out something and how stuff works, while the ebay guys be like "just change bytes 0xB6Ef to 0xE97F to make everything work, isn't that obvious????". Sure, it's obvious if the work has already been done and you just compare the results...
You can reconstruct from the posts at netkas that it took me literally just a few days (counting from my first flashed card ever) to figure out the EFI port mapping in AMD cards thus enabling digital boot screens on HD 5770 and HD 5870 (which I consider a lot easier than sewing a GTX 9x0 ROM together from the scratch). Why didn't the 'geniuses' selling used HD 5870 "VGA-only Editions" for $200 bother to do this before?
Just to make sure that we understand each other, I don't claim that MVC is the only guy in the world who is able build a Maxwell EFI from the stuff which is publicly available, but so far he is the only one coming up with new stuff and giving the impression that he actually knows what he is talking about.