Well, since Apple isn't in the business of manufacturing or designing microprocessor chips in the first place, this would be quite the undertaking, and yes, a LOT of funds would be required! You might as well ask Apple to start manufacturing their own line of mountain bikes as well.
Since you appear to not be aware,
IBM makes the chips which Apple uses in their machines, so if anything Apple would need to work with IBM on this initiative. But I am not privy to IBM's roadmaps and strategies when it comes to its Power series of chips, so I have no idea if they are working on something, what their R&D budget is like, etc. Perhaps another solution to this "more powerful chip in a laptop" problem would be a Motorola/Freescale 2 GHz G4 (dual core?), not a G5...
And to correct you, you imply that Apple is in competition with the likes of Intel and AMD - this is incorrect - Apple manufactures (say it with me!)
computers and AMD and Intel manufactures
processors. IBM is in competition with them, not Apple.