I'd say more like a 50% user base.

I'm going on a limb here, but nowadays, 60% of macbooks (mainly the pro) are used for software development and 30% for creative work (video and editing). While something like half of those professional applications would be fine with the 9X, the other half would be left hanging for a better machine.

However, if they want to make the switch in the near future, I think that the new MacBook will first be released with an ARM processor. This way they won't alienate their core market and they will have a testing ground. Then, I'd predict two or three generations until the pros catch up.

> The only problem is around Carbon

They have the money, if they want to change to ARM it won't be Carbon stopping them.