What are you expecting with this statement? There's not going to be a way to add more faders to most mixing boards, so they don't scale to more channels. You can't add more channels to a power amp. You can't add more inputs and outputs without building a totally new unit.
Just because there is firmware inside the M20d, do you expect that it should be upgradeable to do whatever you might want in the future? This is hardly the case. The hardware is not going to change on existing customer equipment, just like your car doesn't get the new engine that comes out in the next model.
I went through this process with the Panasonic/Ramsa WR-DA7 digital board in the late 90s. Many user requests did make it in to the second firmware upgrade, but a lot did not, because those features weren't possible with the existing hardware.
As others have said, buy your equipment with the expectation that it will always do what it does today---and won't adapt to future situations. It will continue to do the job it was built to do, just as a vehicle continues to do the job it did from day one. My 2012 car can't be upgraded to 2015 standards and equipment either.
"...Having once worked for Apple they would exhibit a similar behavior when sunsetting products."
Doesn't every manufacturer? (Auto companies are required by law to maintain parts inventories for a number of years, but I don't think any other manufacturer need do that.) When a company wants to implement new features---and the hardware won't allow it---then it's time to build a new product. Owners of the previous product either keep it working as it was, or move to the newer product.