With Apple's history over the last few years, I don't expect the sheer amount of legacy software I use on a regular basis to be taken care of when the new architecture comes around. Under legacy I'm also including applications with a single developer that can't really go multi-architecture, applications with niche communities that Apple will take a long time (if they do) getting around to writing drivers, providing documentation and support around porting.
Now the most common rebuttal to this is either Rosetta or that this is how technology works. For Rosetta, just based on the sheer difference in instructions I don't see an easy transition here that works off the bat. IMHO Intel's compiler design also beats Apple's, and I don't see niche apps working right or complete for a long time, and I see a lot of apps being left behind.
But I do understand that this is how technology moves forward, and I think that if they can make it happen (it's still a big if in my mind but I'm aware I know very little here), it will be a big step forward. If anyone can do it today, it's probably Apple. However, I have very little doubt that the transition will be fraught with problems, especially for power users, and it's a personal choice not to live through that transition with Apple.
I'll also add that while I see the strong possibility of personal computing moving to ARM, I'm less convinced by the arguments for cloud. As I primarily develop backends and do cloud arch, I would much prefer to build as close to deploy as conveniently possible.
Now for the iPad part - and this is simply how I feel watching and living in the ecosystem for some time - I think Apple intends to turn the Macbook into the iPad, with one big happy ecosystem of apps that work on everything. While I think this is great for the general public, I'm yet to be convinced that it won't end up with a mediocre experience on everything[1] especially the Macbook. I see the value of a computer that isn't a computer (what's a computer?), but I think that (intentionally) overlooks power-users that use the computer to build things for computers and video and audio professional, to name a few.
1 - With iPad apps being available on the Mac within days of release and minimal developer intervention, I cannot see how it would not be a mediocre experience. How do you do multi-touch on a trackpad?
Again, if anyone can do it it's Apple, but I don't believe it will be an easy journey or one that's going in a direction I can join in. I do still have the option to leave, so I am.