I mean, people used to collect banknotes with interesting serial numbers. Isn't that essentially the same?

If so, you can't "assign" a rarity; a sat's rarity is in the eye of the beholder. Someone might look for sats whose "serial numbers" are divisible by a high power of 10, others by a high power of 2, or 42.

Under this interpretation this means that a VAST majority of ordinals are unremarkable and worthless ("not worth more than the sat they're printed on").