>especially in the embedded ecosystem where SoC vendors just rearrange memory layout and blocks between chip revisions (hey, we'll just update the Linux driver with the latest mappings, that's fine, right?)

This would not be compliant with RISC-V specifications.

There's no boards in the market that I am aware of which run Linux and yet do not follow the boot specifications, which among other things require the use of device trees.

>there's little incentive

... to deviate from the specifications, and opt out of all the benefits of being a compliant implementation.

There's severe costs incurred by not leveraging the ecosystem.