I do not think this is currently possible, but I believe it would be a great feature. The ability to do discounts based on the amount a customer has spent with your store over time.
Customer has spent X dollars over the past Y amount of time from today. They get a Z% discount.
I know a common example of this is in the wine industry, and requires a little more flexibility. In the wine industry, they usually do loyalty based on the amount of cases of wine over a set period of time. That would be generalized as:
Customer has bought X quantity of item (or items from a category for flexibility) over the past Y amount of time from today. They get Z% discount.
I am sure it could be made more flexible, but this is just to get the ideas started and flowing.