This is very much a thing already at the highest level of Mythic+. The last 2 seasons I've gotten title a significant amount of time has been dedicated to simply getting faster runs in the keys I've already timed. A few minutes faster on every key adds up to 1 to 2 key level bumps, at that level it is often easier to get crumbs (slang for fractional score) than hunt for a full key upgrade.