Price set expire on/active on dates relative to event

I reuse one price set for many similar events throughout the year; for each event, people can register early and get a discount, or register closer to the event's start date at full price. A price set's active/expire dates works for this, but because they are absolute dates this prevents the price set from being reused for events with different start dates.

I propose active/expire dates for a price set that are relative to the event start date.