Apart from the added comfort I think most people can see that leaving the middle seat free, when in the vast majority of cases people are seated inches behind and in front of you does not really solve the social distancing problem. Studies done after SARS showed that that at least two clear rows distancing was required to avoid infection. Clearly that is not going to be possible, so we need to find some other solution. The most likely scenario is a basket of measures, for example face masks, testing pre flight and the introduction of rules for acceptable behaviour and probably sanctions for non compliance. Add to this that a number of people will be disinclined to travel because of the risk and uncertainty then it is obvious that things are not going to be as they were before for some while yet.