Re: Dear gods...
"All the major CAD packages had migrated to Windows, what, 20 years ago? And they're not going anywhere for a good long time..."
It probably wouldn't take them long to:
a) dredge out the old code base as a new starting point
b) as needed, migrate back to OpenGL from whatever DirectX schtuff they're using
c) wrap everything GUI in a nice cross-platform toolkit (Qt, GTK, ?)
Seriously, it's not all that hard, just requires some motivation. A tad time-consuming perhaps, but so would Micro-shaft changing their APIs and *FORCING* everyone to use "UWP". And don't think that's NOT in their plans...