Bubble - the £500m sale price of CityFibre - or £500 per FTTP customer even before you connect them. The money there is not on the consumer FTTP, but 5G nodes and the council/large business stuff. The danger is the speculators may start numerous FTTP operators in the hope of being hovered up, i.e. very good at PR and using up lots of cash but not delivering a lot. Now if burning cash gets the UK to a high percentage of FTTP that would be a good thing, but the probability is that this burning will happen in the urban areas i.e. overlap cable networks. The risk with the burning route is that it leaves lot of debt and consolidation and eventually a monopoly emerges with the classic price rises - e.g. Sky satellite TV
G.fast is a way of competing with Virgin Media in the short term, hence size of footprint since it will stop them saying 6 times (or similar) faster than BT and if the latency performance of G.fast is good it might win some back from the cable operator.
On FTTP - contrary to an Ofcom boss, if Openreach deliver the 3 million FTTP they are still in 2020 likely to be the largest FTTP operator in the UK. What happens then is a good question, i.e. will Vodafone take up their 5 million FTTP option, and will Openreach go even further with the FTTP rollout.
Liberty Global so far seems to be not too worried, as if it was DOCSIS 3.1 would be a UK priority.
Bubble also applies to some of the magic around FTTP e.g. zero buffering of video, maybe if you budget on 100 Mbps per customer at peak times, but at some point even with a point to point network capacity is shared. We've even seen some suggest no peak time slow downs.