Something like 5 or 10 years would work well. If an airline can't make the route work, they could then sell what's left of their slot to someone else - includin

Something like 5 or 10 years would work well. If an airline can't make the route work, they could then sell what's left of their slot to someone else - including to a cargo airline like DHL, FedEx, or even Amazon Air. Under the current system, legacy carriers got their slots for free or very cheap so they do wasteful things to keep their slots. They've been using smaller than optimal planes for years, and since the pandemic started the empty planes thing has gotten more common.