A few points of information.
The Plusnet Hub One doesn't support G.INP anyway.
AIUI G.INP on ECI cabinets is only supported for downstream as opposed to both ways on Huawei. Do you know which you are on?
Good wireless in your building may be best achieved using one or more WAPS, possibly connected to the router by HomePlugs. Some HomePlugs also have built-in WAP.
Assuming you mean IPv6, Plusnet have a trial for that which is usually full. While I was on that trial there were also problems with some gateways not supporting it, and you could easily end up on one. I don't know if that has been fixed, but it was quite difficult to get back onto one that worked.
They are also starting to roll out a new network which is not IPv6 enabled, with no published plans or timescale.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 59997/15142kbps @ 600m. - BQM