Regarding antibody testing, it is not clear how soon that will be useful in terms of clearing people to work. Being sero-positive does not necessarily mean one has immunity. It depends on which antibody species. This is setting aside the fact that we still don’t know what immunity means in terms of strength and duration. And there is the danger that healthy people who are sero positive may become lax e.g. less vigilant in their use of masks.
I think any ramp up is going to entail more shift work to allow for less dense work situations. Workplaces will need to be redesigned where possible to facilitate this.