1)"in 18 months time when the connected properties are sold on " I suspect this is completely random timeline picked out of the air. Even IF (and imo thats a huge if) openreach have actually bothered to enable the cabinets that they have "sat" on for 18 months or so without doing anything.
You are also assuming that in 2 or 3 years time (or when /if OR do the required work) that HyperOptic wont compete with BT on price (as given the amount of users, they could well have made profit in that time frame)
Unfortunately I can give you a half dozen examples of BT saying 'no plans to enable that area' for years, then the instant somebody else turns up to serve that area it's suddenly part of their deployment plans. It's aggressive behaviour by an incumbent to say the least but it happens.
The fate of Invisible Networks in Cambridge is a standard template for those cases...
I do assume that with good reason, I've worked for a large number of ISPs (some of which played the 'lit building' game like this and jumped ship because it was financial suicide to continue) and there's a reason why many of those ISPs have decided business services are the future - BT / VM will always win in the consumer market.
Unless you have tens of thousands of customers and can afford the initial cost of outsourcing your support to call centres staffed by flow chart monkeys (UK or abroad) then you can't compete on cost there and unless you serve such massive user bases you can effectively contend backhaul and transit to avoid the true cost of bandwidth you can't compete on cost there.
Most people don't need or want 100Mbps+ broadband and it's a couple of % of people who'd ever dream of paying £50+/month for internet access alone.
You can't grow and make profit in that industry any more, it's not the 90s anymore, the only way you grow is to plough millions into infrastructure at a loss for years and that's no guarantee of success.
Hyperoptic might survive and make profit as a niche player in a few areas but that's about it (and if they do then a established provider will likely buy them to make some money out of the synergies).
I know that's *really* doom and gloom but I know the industry very well...for consumer broadband, it's curtains for anybody who isn't already huge or established in a niche...