Is coreboot for framework actually being worked on in earnest? My googling only turned up that one guy was doing some basic work on it but only as a concept.
The Chromebook editions use coreboot already, it shouldn't actually be too hard to get it to work on all editions (for Framework). I guess they just have other plans currently.
The Chromebook version comes with coreboot because that's a requirement for all Chromebooks. It would be nice if all editions had that, but IIUC the Chromebook's motherboard is also a bit different.