General DSL Support

What are the main challenges in supporting a DSL modem? I believe I have heard before that most DSL drivers are closed source, is that the main barrier? Do we need a manufacturer to release a driver to the community (similar to the genesis of the mt76 project) before we can really see widespread support for DSL modems?

FOSS drivers.

you can use a technicolor Modem/router Like
TG789vac v2
They are all runing on Openwrt Chaos Calomer 15.0.1 and can be rooted with several exploits.
see here :
or here :
Once rooted you can do everything you want with hardware NAT and an optimized DSL driver (Broadcom)