Unfortunately, it seems like you're STILL missing my point. What you described above is actually confirming my message. I'm not sure how to make it simpler to understand, but I'll give it one last try...maybe the 3rd time's the charm:
Tesla is offering you the ability to drive up to a service center, hand them $2500, and leave with a PURPOSE BUILT MODERNIZATION SOLUTION that TESLA developed and installs themselves, all in a single package, no extra thought required.
BMW (and others) do not offer this. What you're describing above is just BMW using the same I-bus protocol over the e46, e39, e38 (etc) platforms, NOT a PURPOSE BUILT modernization package. Yes, you can swap out components if they're all communicating via the exact same standard as long as you have cables to throw the data to the right pins at the source and destination. But once again, convenient cross compatibility is NOT a purpose built modernization package like Tesla's offering. Which is my point.
Your article from e39source shows how basic this is when they mention that "Any mix and match will be compatible, though the graphics may be stretched or compressed to fit the different ratio displays." This isn't BMW designing a retrofit kit, this is just the screen displaying a raw video signal it receives, unmodified, stretched/compressed to fit within its physical limitations.
While this BMW example wasn't the important piece I was trying to get across and we're super into the weeds, the point is that while other manufacturers may have parts that work together over a few model years, they do not typically have packages that allow you to walk into a dealer and pay for an upgrade that makes your 7 year old car work exactly like a brand new one.
Cross Compatibility Installed Yourself =/= Factory Purpose Built Modernization Package