[joezydeco]

It's better than the opposite, which is designing to some random processor with completely opaque information about it. No datasheets or TRMs, no idea of production schedules, no idea of lifespan.

And I'd classify Samsung Exynos and the Broadcom BCM2835 in Raspberry Pi in that group.

[eldondev]

Well, I hate the opaque bits of both those, but that doesn't mean an upgradable board can't be designed around the specs they implement, and those chips are just the commodities that populate them. Write your code for ARM, make a good pin-compatible interface that can allow for replacement with other components if necessary.