ADSL is pretty old yes, but still in use in many countries. VDSL2 is becoming more common and is still being improved, See wikipedia.
TP-Link have many ADSL & VDSL 1/2 routers available. Sadly their firmware doesn’t seem to work with IPv6 /56. I very much doubt they managed to get theirs certified, at least not fully.
But anyway, if you do produce a model, please let me know. :).