I just spoke to CU Athletics, and got some additional information.
Once they figure out how many people will be allowed at games, they will design a seating map for the stadium. Their plan is to divide people so that you won’t have people in the rows in front or below you (I guess by a few seats) or next to you on either side. Once they figure this out and know how many people opt in for ‘20, they will offer opt-ins available seats. Per CU, if you don’t like what they offer you, they will let you push over to ‘21.
If you opt for ‘21, you can put your Buff Club donation to ‘21 as wall (i.e. you won’t have to make a ‘20 Buff Club donation, but you can if you want, obviously).
You can switch to Spring if they move the schedule an you opted for ‘21.