Seems to be the obvious thing to do and has been for decades.
I'm almost at the point of suggesting that 999 call-handling should have some rule-changing, to be honest.
Everything in my workplace is IP - from the phones on the desk, to the fax machine, to the GSM alarm systems to the SIP trunk. There are no longer any analog or ISDN lines or anything of the sort still active, because there's no need for them to be and they have disadvantages despite being actually on-the-premises still.
Its seems only logical to plan for an IP-only future in terms of telecoms, even things like video, mobile telephony (all modern handsets do SIP, so the 4G etc. network is really only providing a data backend), etc.
I imagine it means a lot of clutter removed from exchanges and only legacy lines having a kind of conversion equipment, which can be phased out by moving everyone to "proper" fibre connections as necessary.
It just makes much more sense.
The get-out-clause also disappears from BT's books - they can't just blame demand for not having cabled your area properly yet. If you have all-IP exchanges and all-IP cabinets, there's no reason that some manky old line can't support stupendous speeds even if it's shared with the rest of the village once it gets to the exchange. That won't stop them trying, though.
I can quite easily believe now that there are households and businesses all over the country that are pretty much IP-only, internally and externally, for everything from telephony to CCTV.