XG has been completely abandoned, as far as I know.
The last products i'm aware of that still did it were the genos2 (successor to Tyros) and the PSR-SX920. Between those two, you probably have the most complete XG patchsets if you can get them out of the ROM.
They have not abandoned AWM2, though, as current products still use it, with the Montage M having an "extended" version.
The project being worked on i'd consider as legal as nuked-sc55 is. bring your own rom dumps/TBL files.
Roland and Yamaha seem to both recognize that the current soundfonts and wacky projects floating around are not affecting the market value of their current stuff. They probably aren't that happy about those silly kontact libraries people have hacked up and sold, but they are still around and still somehow being sold... Roland appears to no longer make GS devices, and only the arranger keyboards seem to even handle GM2 now. Yamaha makes no more xg products. Neither makes tone generators anymore at all, so there's no sales to canabalize anymore.
The roland GS sampleset seems to be available to sublicense from Dream, under rather restrictive terms. i'm not sure if there is any other way to license the full quality samples at all, and roland+yamaha aren't the easiet to talk to. I had ask ed Roland about SOund Canvas VA and improving it, and they never really committed to anything
The real issue with the project may be that AWM2 is protected by patents. And some of these were filed in 2015. A careful search of the patent databases is needed to determine if the MU2000EX is itself protected by any still live patents. The Extended AWM2 implemented in the Montage M is definitely still protected by patent. The earlier versions used in the MU units may not be, but your own software implementation of AWM2 will have to respect the current patents. This is why i wanted to drop better samples into S-yxg50 VSTi. 😀