No DKMS, ever. All our drivers are headed to mainline. I'm not even going to bother with DKMS most likely; people who want to use bleeding edge drivers before they're merged can use our kernel trees (and we'll have builds available for those folks).
For the reasons you say, I personally would rather buy e.g. some pine64 thing just might benefit from this porting work. (Probably more in the userland than kernel itself, tbh.)
The one good path I see for hardware is that in the system on chip era, open designs can gain a foothold by saving the companies money, just as no one could compete with free linux for server software 2 decades prior. There was no hope getting a foothold with 1 design = 1 chip, but a world where people can mooch some free IP for their dohicky might do the trick.