Sammy's problem lens is an Art lens. Not a dated glass fossile.
And I doubt that Sigma stopped to service any of these two, neither the 30 mm nor the APO 300 mm. In Sammy's thread opening was no single word of a firmware update, so I wonder why you bring up a different issue, but it appears that any problems are welcome to you as long as it's bad for Sigma.
Also, I can get spare parts of a 20 year old Gitzo, but some accessories don't work together with a current one - it's just normal and the stealth name of these processes is "innovation". Don't blame me...
In any way, incompatibilities are no specific issue to few manufacturers but to the whole market. I doubt there will be a Nikon D980, there are many patents of lenses for a curved sensor = mirrorless = DSLRs will not increment any longer. But you know what? Sigma's unique decision to offer not only a dock but also a lens conversion service will become rather interesting in the future - getting a native mount is much cooler than working with adapters, I hope. I'm quite happy with my investments in this brand.
Feel free to keep on working on a bad reputation for Sigma, without any experience with Art or Sports lenses (you didn't buy the 150-600 from Sigma, if I recall correctly?). And I keep on teasing you in this attempts, nothing better than foolproof routines and discussion patterns