Our real-world usage
* My wife uses her iPad Pro exclusively (she is the full time manager of our home life)
* Our 10 year old son uses his iPad 99% of the time (once every couple of months he plays a game on an iMac)
* Our 14 year old daughter games on an iMac most days and everything else is on her iPhone, even school work. She almost never uses her iPad.
* I use my MacBook Pro for hardware and software development, some macOS-only financial reports, and bulk photo processing. Everything else is on my iPad (even some script development).
Our son could easily live without a Mac. Our daughter lives without an iPad. I need both. So amongst us, given our life stages and interests, it’s 50-50. I don’t see anything happening the next couple of years that result in us eliminating Macs.
The main difference the iPad has driven for us is we no longer need two Macs and our Macs will last longer (our 5 year old iMac is still doing surprisingly well playing games). There is also an implication for my backup strategy as more and more data shifts to iPads — even my code is in iCloud (as well as on the Mac and Github). My 12.9” iPad Pro is awesome but it can’t compete with the development productivity having an ultra-wide monitor, true windowing, background tasks etc bring. I don’t see any way this is going to change in the next couple of years. I think if Apple made a strategic shift to enable this kind of thing on iOS it would be a huge mistake for the general iOS user base. I can see them making some moves to support development but not to the point of trying to replace Macs.
I am not sure what impact the advent of iPads has on Apple’s share-of-wallet. The iPads are personal devices so each person needs one (for our family even if the iPad had user profiles this would still be the case). The upfront cost of iPads is marginally cheaper than buying a couple of Macs however Apple is driving a faster refresh cycle on iPads. The rate of improvement of iPads vs Macs makes it hard to resist regular upgrades (at least for the parental units) and in practice I think these costs will exceed a Mac-focused approach.