We have been working with 5.1 for months, but nothing has changed in relationship to DX12, is not that 5.1 made it any easier or less risky to use, so won't use it.
However, the big news ( from an SDK point of view ), is support for HTML5 rendering, which replaced the old Scaleform based on Flash technology.
The ATC/Simconnect menu is now made with HTML5+Javascript and the first advantage is that we should finally stop seeing issues with the "GSX menu", that lead to crashes when opening the GSX menu ( it's not the GSX menu, it's the ATC/Simconnect menu ), which contributed to spread the urban legend that GSX can crash the sim ( it can't ), what was crashing in 5.0 was the old Scaleform menu, which is a technology that has been bought by Autodesk only to get rid of it. And Flash will officially die forever in early 2021 anyway.
While there will be an immediate gain in stability with the new menu system, the more interesting thing for us, is that HTML5 is supposed to work with RTT too, which means we might possibly be able to do the same things we used to do in P3D4 using DirectX 11, but in HTML5, which is surely easier to use, faster to develop for, and hopefully less risky. This feature ( RTT with HTML ) has been added very late in the Beta, like a couple of weeks ago, so we didn't had any time to really test it, and is basically not documented yet, other than having got a verbal reassurance from LM that it should work with any kind of scenery or vehicle object.
This doesn't mean you can expect a GSX update to get back custom logos over vehicles or active panels very quickly. The feature is new, we haven't really tested to see if there are any possible issues or performance problems in a real world situation, and there would be a whole new piece of code to write for GSX, to replace what we used to do with DirectX into something using this new system.
