Cheetah was 10.0.
Puma was 10.1
Jaguar 10.2
Panther 10.3.
(Yes, I'm nitpicking.)
I'm pretty sure that Apple won't make a 64bit processor the only supported processor before the last G4/G3 sold by Apple is at least two or three years old. Take a look at the age of the newest unsupported machine by 10.3: The beige G3s. When were they last sold by Apple? (Checking apple-history.com...) Ah, yes: January 1999. That's almost five years when Panther arrives. And with the G4 processor going strong (the iBooks are even believed to still inherit the PowerBook's G4 processors when the PowerBooks get higher end G4s or G5s) in PowerBooks, iMacs and eMacs, we can - quite safely - assume that our G3s and G4s will still work with OS updates that come out in 2007 or even 2008. Okay, they might be obsolete machines by then, anyway, but hey! You asked...
I think Apple has a good 'window' open for 'currently supported hardware'. I don't want to buy a new computer every year (well, okay, I want to, but I can't...), but I also think that for beige G3 owners it's either time to get a new computer or, well, stay at either Jaguar (which runs fine for such old hardware) or Mac OS 9.2.2, which is quite a fast OS on those machines. If you want to prevent those machines from being doorstops and have NO idea how to live without the newest updates, install a version of Linux and make the thing a file-/mail-/proxyserver.