Agree. But will need to board assigned seats before even pre-boards. My guess is even $20 will prevent 90% from getting assigned seats. Perhaps for an exit row or bulkhead for some or someone that checks in 60 min before flight time (and will get a C) for a long flight. But I think they will only have about 10 Assigned seats per flight, if that many.

As to selling snacks -- too much paperwork, etc. for the effort. Maybe a "sack lunch" for flights over 3 hours, where FA have extra time and people more likely to buy. Probably airports will not allow, but airlines would be better off selling a sack lunch (with 3-4 selections) in Gate Area. Most places have 4-8 gates in same area and most pax are sitting around anyway.
Then no hassle with sales, change, etc. on board, more selection, less waste, etc.