I agree they are not insurmountable. But 1) it's a big failure of the Brexit campaign not to have discussed them, never and 2) hard to imagine a trade deal, or any deal, will be agreed before these questions have been settled.
These people do not have a VISA right now, they don't need one. And one day, overnight, they will presumably need it. What criteria will they need to satisfie and how long will they have to get it? This is something they don't know, nobody does not even the Home Office, and I bet is giving them immense stress.I still don't understand the justification for your comment that EU citizens will be sent back.
What about those with job, house, family, friends and everything else? Right now they don't know whether they will be allowed to stay in the country.