Generally:
Modemrouter with Broadcom chipsets are not supported because they have proparitäry drivers only.
Devices with Lantiq chipsets will support or it exist a teoretycally possibillity to support them because they have proparytäry Modemfirmware (that can be extract from RouterFW) and Opensource drivers.
Support for VDSL2 Annex Q profile 35b (Aka Supervectoring) Modems does not exist in Openwrt.
One Theoreticly candidate of Suppervectoring support in future are the Fritzbox 7530 with Lantiq VRX518 Modem but:
- I am not shure but i thing it exist some difficult problems to support the Modem.
- I fear there is no manpower to develop VRX518 modem support.
For this reasons i have no hope.
Support of normal VDSL2 Modems up to profile 30a exist in target=lantiq and subtarget=xrx200 devices.
But only for speed between 50-90Mb/s.
Analoge telefon FXS connectors work with Lantiq SLIC-1xx chipsets.
One VDSL2-modem-telofon-router are the O2-Box 6431.
Another xrx200 router with more resources but not only supported by a fork are the Easybox 904xDSL