If you detect anything older than 802.11n, change channels or start knocking on doors.
What is a problem is that the preambule time is wasted, but it would not be too hard to imagine that even this preambule could be used for newer amendments after some homework.
IMO the entire 2.4ghz public spectrum block should be viewed as for legacy support. However far more spectrum should go to limited range use. (Also, building walls should have filter meshes that absorb frequencies not designed for use with mobile computer to cell towers / GPS).
You neighbour's 802.11b will never see that another Wi-fi network piggybacks on him and goes 100 times faster. There is even not the need to use the cumbersome CSMA/CA.
Indeed it is not an existing amendment, but if you are interested I would be happy to help someone to present a few ideas at IEEE 802.11.
How do you expect the "knocking on doors" part to go?
"Excuse me, something using an old wifi standard in your home is stomping on my speeds. Could you either turn it off or replace it?"
But if you did want to force someone to upgrade, you could always jam them... pretty easy to selectively jam a radio. Or crack their WEP (most 11b)... So many bad things.