Most people who want a router with open source firmware get one that's compatible with OpenWrt and use that, is there a reason you don't consider that to be using open source firmware?
I love my wrt54gl as much as the next guy, but I hate having two devices to connect to the internet instead of just one.
For OpenBSD on Orange France FTTH: https://lafibre.info/remplacer-livebox/remplacer-sa-livebox-... or https://try.popho.be/securing-home2.html
The last time I searched for open hardware, even the implementations running Linux on a desktop PC with a caux adapter were not DOCSIS 3.X compatible.
The companies that multiplex the signal down the cables keep updating their standards, both a blessing (for speed) and a curse for maintained code
VDSL2 Modem with Kernel support. With OpenWRT and mainline Kernel its able to push roughly 100Mbit/s over WAN.
I wonder if I can find a device not fully upgraded