I think for most people 16GB is more than enough to make modern music – but not orchestral. (But it really depends on the case…) Although I have to say that for many years as a student I have worked with 8GBs only, and I still put bigger productions out there. But it was a lot of printing, going back and forth. Not a lot of fun. If you have more room to play with, you enjoy the time much more.
I don’t think that many professionals will switch to new machines in the near future. I think just having a Mac that’s the new solution (students, blogs, etc.), but for professionals, especially studio-type of work it’s not what you actually want now.
Then there is always the compatibility issue with all the DAW & software that all of us hate if it doesn’t work as it should. I would say that from now on it’s maybe 3-5 years where some of us could really think about those new machines.
One of my friends said that he doesn’t support that Apple is doing its own chips due to “monopoly” etc. But I guess that for the customers it will always be better if you have a device that was built “intern”, and not put together by 3 other companies. And as prices show, Apple could even get a little cheaper which a lot of people are still discussing that Apple is too expensive compared to other companies.