I think that whilst borders may open again at some point, the point being missed is that most Europeans, can, if desired, hop in their car and pop over a border or two to holiday. For us Brits it is not that simple. Until we allow mass gatherings again then I can’t see how the government is going to allow 170 people on basically a small tin box and more importantly, tens of thousands of people into an airport. There is no indoor gathering more mass than an airport. Social distancing is virtually impossible. There have been rumours in the education environment that schools will reopen end May/early June but they are fully preparing for them to shut again in November/December as we get hit with another wave and the NHS is busy at that time of year. I would imagine ferries would be a similar and there will certainly be no cruises based on what has happened with those.
You then have to factor in insurance and the likely lack of cover for Covid related problems. This becomes a huge problem, particularly after we have left the EU. Anyone who plans to travel without cover that will pay out for Covid related problems would need to be certified because I can only imagine what a 2/3 week stint in ICU abroad would cost together with the air ambulance home.
I therefore can’t see any holidays abroad until at least 2021 and it may be well into that year too.
For the UK, they have the problem of mass gatherings too. If they suddenly allow people who now can’t go abroad, to go away in the UK then seaside towns, campsites, the Lakes and the like would be completely overrun with people. Again I can’t see them allowing that.
I think it will be vaccine or cure needed to get things fully back to normal. In the meantime they will loosen lockdowns and then tighten them again when numbers spike.
The outlook doesn’t look great at the moment for me so I wouldn’t make major plans for anything until this is over.