If they could invent a face mask allowing social distancing down to two feet then we could kill many birds with one stone.

Then we eliminate middle seat bookings except for family members filling a row. Eliminate recline (to keep pax' heads spaced evenly!).
1. Substantial passenger loads can be sustained.
2. No more arm rest fights.
3. No more passenger of size conflicts.
4. No more need to gate check carryons.
5. Unfortunately it would be necessary to resort to astronaut style food, like instant breakfast and soda straws.