Do you think when Surface Book 2 comes out, Microsoft would then sell bases only so we can use it on our Surface Book? It's a good way to upgrade for newer GPU, better battery or even enhance hinge. Surface Pro 4 keyboard has backward compatibility to Surface 3. I hope Microsoft would do the same.
1. MS can't manage to get the original 'specifically designed' duet to work.
2. Configuration management is a bear in the real world. I can't imagine MS wanting to support this kind of mess when they apparently don't want to support even the pristine designs.
3. MS was trying to get beyond having bastard builds and provide a 'This IS The Standard' experience.
4. From the descriptions I've seen, the GPU is meant for a far different screen, etc. This is not a rack mount device. You're probably not going to see that big a difference.
I'd settle for knowing MS was readying original bases for swap out when everyone exhausts their battery recharges and aren't ready to pop $2k for a new laptop or really have no use for a 2 mile extension cord 'laptop'.
Even a MacBook Pro has some replaceable parts when it goes off warranty and you want to fool with it. The SB is a sealed coffin.