Chen, is i.MX8 a realistic option, or is the hardware design way more complicated to the extent that it would pose a risk to the project?

Asking because I'd happily accept a device that is slower but can run a mainline kernel without blobs that tie it to a specific version. Having a separate baseband appeals too. I'd probably pay more for this.

Having said that, I'd settle for a "mostly free" qwerty slider - that's infinitely better than no qwerty slider!