
 :Because of some contract, IBM is not allowed to sell its
 :486 chips to third parties, so these chips are unlikely to become
 :available in any non-IBM machines. 

I saw in this months PC or PC World an ad for computers using IBM's 486SLC.
So I don't think IBM is restricted in selling their chips, at least not
anymore. A clock-tripled 486, even without coprocessor would be great,
especially with 16k on-board cache. Make it 386 pin-compatible, and you
have the chip upgrade that dreams are made of :-)