The Red Cross and the regional blood bank in my area both test for COVID19 antibodies. Seems extremely unrealistic that testing infrastructure would be too difficult considering how much we've done for the pandemic. "Just jab everyone and we're done!" sounds like a desire for a simple silver bullet solution, which is a very common Silicon Valley way of seeing the world.
Equating antibody presence to be the same as having been vaccinated would give health officials a much more accurate view of the pandemic and where resources need to be allocated instead of this odd ideologically driven need to demand conformity from everyone even if they already have immunity that appears to be an order of magnitude more durable than the jab. It makes clear that this is almost entirely about a pathological need to round off all the corners in the world and almost nothing at all about fighting the pandemic itself. But what a wonderful opportunity this pandemic has been for the authoritarian types. For them, this truly is the golden age and should be extended for as long as possible.