Yeah, aside from hardware support (bluetooth, wifi, and flash) and the obvious extra features Linux could bring, having a fully free firmware is a goal. And yes, it would be possible to distribute disk images like openwrt or similar projects do.
Potentially this kernel could be used on other targets - Agptek Rocker, Eros Q, and the xDuuo x3ii & x20 IIRC all have bluetooth and/or wifi, and could easily make use of this since they are X1000-based. So the benefit to rockbox overall is potentially bigger, and this kind of thing could even be a viable way to get new ports - assuming that Linux mostly supports the SoC, it is a lot easier to get Linux running than it is to port Rockbox to a new SoC. But this is all just wishful thinking on my part, of course I won't be doing any of it.
Anyhow, I went ahead and built a bootloader for you. Should be OK to flash if you want - as far as I know there's no regressions.
https://drive.google.com/file/d/1pPEhtWrn_hWLLqwWhdxmp2zPbUwhhRhU/view?usp=sharingHopefully gerrit will be back up soon, so I can get this and multiboot merged.