It's also a provisioning problem. Let's assuming that the new pricing model is based on usage per user, like 50,000 records per user, and how are you suppose to track each individual record, even that is possible, it would not be very practical as the every CRUD operations would require a record count referenced to the user. Keep X records per Base makes the operation a lot easier and technically much more feasible.
I wouldn't suggest anything so complicated. Rather (if it isn't a technical limitation), I'd suggest they increase the per-base limit for customers who pay for more users, or else add a third paid tier above 'pro'.
