My neighbor was directly involved in running several of the mobile testing centers over the past couple of months in Mississippi. The scuttlebutt he's hearing as of late is, to paraphrase:
-Regarding antibody testing, nearly everyone that has been tested multiple times for antibodies will show the antibodies on the 1st test, but not the follow up some period of time later. They began to notice this when they first started antibody testing in the early stages, mainly of the nurses and workers. His anecdotal opinion is that the antibodies won't be lifelong, or even for an extended period, which falls in line with how other coronaviruses behave. The reason you don't get them all the time is constant exposure i.e. letting your immune system do it's job.
-His opinion, like you alluded to, is that this will in fact (like many people mentioned in the early stages) become just another disease we must contend with as we do other diseases. Once it burns through (hopefully controlled) the population as a big wave, hopefully it will become more of a seasonal thing with less impact.