A proposal for reducing routes due to multihoming

Bill Simpson claims that this idea is ~10 years old, but if so perhaps
it's time to air it again. I thought of this during the route flap BOF at
NANOG, mentioned it, and nobody came up with any immediate reasons why
it wouldn't work, so I'm sending it to the list for further consideration.

It's dead simple, really: Assign address blocks to pairs of providers.
Both providers announce those blocks all the time, and assign addresses
out of those blocks to customers who multihome between those two

What if the customer ceases to be multihomed? Reassign it to another block?

On the other hand, if a client starts operating as single homed, it will
have to change Ip addresses when getting multihomed.