That's why filtering /20 only without re-aligning the holes in the block won't work. In the end /20 make the routing table looks pretty but they are black-holing lots of traffic.
Well, it won't. The proposal for filtering is to filter on assigment boundary, and for swamp space filter on /24. Now, what will break is people punching holes in their PA space for multihomed users. Funny enough, this has never been discussed (to my knowledge) as a problem in PTOMAIN WG of the IETF. There the argument was for traffic engineering and commercial relationships...
As we all agree that re-assign address is NOT practical at all thus just filtering /20 block is not a good solution.
That is not the suggestion. See above. The assignments per block and RIR is well known. Best regards, - kurtis -