Since I may one day need to finally leave my own MS Access EMR to buy AC, I'll chime in. The fairest policy would be to emulate Microsoft and most other "off the shelf" programming platforms and sell AC licenses with consecutive use limits.
For example, if a provider buys 2 licenses, then a maximum of 2 users would be able to log into the back-end tables at the same time. That way, you can have 40 doctors working consecutive schedules of 1 hour or 1 doctor working 40 hours straight... the overall use of AC would be the same, and the cost should likewise be the same.
Seems simple enough to me, and results in overall fairness. Licenses can thus be all priced the same since they simply add functionality rather than get caught up on how many physician pockets one can pick, some of who may hardly use the program at all. Oddly enough, I think that this arcane idea of one software to one user is only seen in EMRs and with Dragon Naturally Speaking (which likewise rediculously requires a different license for each dictator, even if they all use the same software on the same machine).