Maybe this is getting blown up by the media, but I've seen a lot of tech people in the UK on HN and elsewhere looking (sometimes desperately) for other opportunities. Even if future agreements don't make it harder for them to remain and work in the UK on paper, it may still cause a lot of skilled labor to leave the UK purely due to perception.
That's assuming that it remains just as easy to do so, which seems unlikely given immigration was part of what was driving the leave vote. Even if it is still easier in absolute terms for someone in the EU to work in the UK than the US, the lowered differential could have pretty negative effects on the market for high-demand jobs.
Really? Because I explicitly remember that running a company and dealing with other European countries has been hell of paperwork, lawyers, different standards and protectionism which made running a company that sold goods or software across Europe extremely complicated before entry of the coutry into EU in 2004. Just the standardization of financial (global VAT system, unified taxes, etc.) and regulatory (if an item is legal in one EU country then it's legal in another) has brought so much more commerce, jobs and startups that I doubt people in this topic born after EU can even fanthom.
That's assuming that it remains just as easy to do so, which seems unlikely given immigration was part of what was driving the leave vote. Even if it is still easier in absolute terms for someone in the EU to work in the UK than the US, the lowered differential could have pretty negative effects on the market for high-demand jobs.