Rigiht, so...
My current setup is a small Linux server that runs PPPoE through an ADSL2+ SpeedTouch modem (configured in bridge mode). Are you essentially saying that the same PPPoE setup on Linux can be used, with BT's VDSL2 router plugged into it instead?
Yep, and you can have some of the best IPv4/IPv6 dual-stack routing support available. The set up you use is the most flexible really, the WAN protocol is relatively irrelevant if you have the correct software set-up

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And CentOS/RHEL isn't bleeding edge, but it is ultra stable, and fast. Exactly what you want really. Add EPEL if you want newer stuff.
It should be rather smooth for you, and no additional expense above the standard installation costs.