Re: The elephant in the room
This all presupposes it actually becomes as hard for skilled UK workers to head to the EU post brexit as the UK wants to make it for EU workers coming here.
That one is easy to fix: just impose exit visas. Another useful approach would be to make student loans (with a suitable early-payment penalty) automatically due in full on the date you take a job abroad. Another option would be to make passport renewals for overseas resident cost a fraction of their income.
The possibilities are endless if you put your mind to it.