I'm allowing myself to be optimistic to the point of booking a trip to the UK and France in August. Granted, it's little skin off my back to do so - this is a trip I had scheduled for summer 2020 that was canceled, so I'm sitting on airline, rail, hotel and other credits. And with all these credits, I'd be able to cancel and reschedule everything again if need be with little inconvenience. If August is approaching and things look good, I'll proceed as planned. If, by June or so, it looks like things will still be uncertain or the trip would just be too... weird... I'll postpone again.
For government authorities and the other powers that be in North America and Europe, I'm inclined to think they're looking for an opportunity and excuse to open things back up and offer folks a semblance of normalcy. We see that to a certain extent already, even - when infection, positivity, hospitalization, other leading indicator rates allow, businesses and schools can operate at such and such capacity, with more lenient restrictions, etc., in the absence of anything approaching herd immunity or even having spread under control. The bar is low and we're all being graded on a curve, in other words. We can discuss just how effective (or ineffective) that's been and how many problems that approach has caused, but ultimately I suspect once vaccination is moving along at enough of a clip to give decision makers cover, we'll see travel restrictions disappear or become significantly less strict (perhaps proof of vaccination and a negative PCR test and you're good to go, for instance) because they'll have decided that's what economic concerns and their constituents demand.
Of course, rules and restrictions are only part of it for me. I also want to feel safe for my own sake, and not feel like I'm posing a risk to anyone I come across when traveling or anyone I return home to. That'll be a judgment call I'll have to make when the time comes, regardless of whether destinations have quarantine requirements or open borders or capacity restrictions. Further, as mentioned earlier, I just don't want my trip to be overly "weird" - I don't want too many places being closed, options being too limited, and left feeling like I can't actually relax or be allowed to occasionally if even inadvertently let my guard down once in awhile. Time will tell if August will allow for that. Again, though - I'm optimistic. It's a cautious optimism, complemented by backup plans :)