I don't see how manufacturing the old chips would be a problem. All the necessary logic could now be contained on a single die, and I doubt any semiconductor company would turn down a paying contract. If that is the case, though, it could be done easily on a PLD, although that would increase the cost of the mobo by about US$60. The old chips could always be recycled, too, but I guess that's not practical.
Anyway, I guess it's kind of a moot point anyway if the A1 is indeed intended to be a 'fresh start' for the hardware.
I'm not yet up to date on what's been going on with the Amiga (a lot has happened since my A500 days, and it's a bit confusing), but I was under the impression that we wouldn't see a completely new hardware philosophy until OS5. I guess I was mistaken.
Of, course at this rate we won't see OS5 until 2010, so I guess the A1 will be around for a while, and I guess it wouldn't be good to saddle it with 'legacy' hardware.
And yes, I realize I do a lot of 'guessing' but that's because I don't want to sound like a know-it-all. This really isn't my area of expertise (yet) but I have at least a passing understanding of computer electronics.