I think it's a great idea.

Sure, you can use miles for UG (when the bucket is open).
or
You can buy FC or (full coach->FC).

For a non-refundable fee, a consumer can be placed at the front of the UG list.

No guarantees, just for the non-refundable fee, you get moved to the front of list. First come, first served.

Silver - $150
Gold - $100
Plat - $50

The other standard elite UG protocols would remain.

So, pecking order:
1) FC purchase (via cash or miles)
2) Internal Operational Upgrades (pilots off to work, FAM, misplaced pax)
3) ** NEW ** PriorityUpgrades
4) Std Elite program

Sign me up! Good for pax that want to use it, good for the airline (might cover the drink service costs in FC).