LostToucan
How does that solve the Beaufort’s Dyke issue?
It might not solve the issue - the feasibility review hasn't been published yet;
High Speed Rail Group (HSRG) has proposed tunnelling under the Irish Sea between Stranraer and Larne in its submission to a review led by Sir Peter Hendy, who is expected to publish his interim report within weeks.
The two towns are 31 miles apart but a preferred route for the tunnel, based on 120-year-old research by the Victorian engineer James Barton, would be diverted to avoid Beaufort’s Dyke, a 1,000ft deep trench in the Irish Sea.
www.theguardian.com/uk-news/2021/feb/14/rail-bosses-revive-plan-to-build-tunnel-from-scotland-to-northern-ireland
mathanxiety
Do the architects/advocates of this scheme know where Portpatrick actually is? Have they ever visited the village by car or public transport?
I assume local councillors have visited at least;
Feb 2020 - Dumfries and Galloway Council said it was "certainly not averse" to the proposal [bridge] being examined...
www.bbc.co.uk/news/uk-scotland-south-scotland-49661019
"We have had winds of over 60mph here, on a daily basis, for the best part of a week. The frequency of high winds here is increasing. How would a bridge in the North Channel cope?"
To be fair, the architect is now proposing a tunnel, rather than a bridge - as per my previous post/link.
the London-centric Tories
the then Tory-controlled Scottish Office
The readers' letters in your lengthy c&p (published in The National - The Newspaper That Supports An Independent Scotland^ to quote the heading in your link) fail to mention that the SNP MP for the area lost his seat to the Scottish Conservatives in 2017. Alister Jack (the current MP - Scottish Conservative and Secretary of State for Scotland) seems quite keen on the idea of a tunnel (less keen on a bridge). I doubt he is completely out of step with his constituents - there must be some local support. Fun and games in the local council as well;
Sept 2020;
Former SNP stalwart switches to Conservatives over concerns about Scottish independence plan. Councillor Andrew Wood has quit the Nationalists and claimed they had become "a far-left extremist movement". 
www.dailyrecord.co.uk/news/politics/former-snp-stalwart-switches-conservatives-22717941
Ever heard the phrase 'joined up thinking'?
Dec 2019 [EX] TAOISEACH LEO VARADKAR has said the Irish government will not “dismiss or pooh-pooh” the idea of a bridge being built linking Northern Ireland and Scotland...
The Taoiseach told reporters...that he “knows people dismiss these things out of hand, but they used to dismiss the Channel Tunnel as well” prior to that being built.
The Taoiseach admitted that he has spoken to Johnson about the bridge idea.
“We actually chatted about that the other day when I spoke to him after his re-election as Prime Minister and I suggested that I thought it was an idea worth examining and that we should take a look at it but I expect the UK to pay for it..."
...[Varadkar thought] a “high-level engineering assessment” should be done to see whether it is a viable proposal...
He cited the Channel Tunnel, the bridge linking Denmark and Sweden and the recently-completed bridge linking Macau and Hong Kong as examples of large-scale engineering projects that have worked.
www.thejournal.ie/leo-varadkar-bridge-boris-4946052-Dec2019/
These ideas about a bridge/a floating bridge/a tunnel, are all predicated on the notion that there will be an economy in NI by the time any of the dreams come to fruition.
Don't write off NI yet - we are only 7 weeks in.