Although Intel has never talked about the development of a 32/64-bit hybrid processor, it's been rumoured for quite some time that the code-named "Yamhill" CPU is just about that. Much like AMD's current Opteron & the upcoming Athlon 64, Yamhill would provide 64-bit extensions to Pentium 4's and Prescott's (Pentium 5?).
According to this report at The Register & taking the word from investment research organisation, American Technology Research, Yamhill won't make its way until 2005...
Athlon 64 will set the ball rolling, but we're not yet convinced that it's going to grow AMD's market share dramatically enough to create a 64-bit mass market.
However, a similar technology from Intel would accelerate the process, if only because of the weight of the company's marketing machine. Where AMD largely has to wait for market momentum to build up slowly behind its 64-bit technology, Intel has the power to get the market moving itself.
With Intel keeping its mouth shut for now, it's too early to tell. We will have to wait until AMD makes its move this September and depending on how the market reacts, the chip giant will most likely accomodate its schedule (assuming Yamhill development is in good shape already), for now they won't want to affect Itanium nor Pentium4 sales.