Your description sounds close to the Surface Book. I'm suprised Apple hasn't come up with a contender. I guess the market for that kind of device is just not big enough for them?
I think most people looking for a "laptop" just aren't aware, how useful a pen is. They don't think "annotate everything", anymore, even tho they grew up like that. Their mind has grown bend over the laptop.
The device itself isn't all to the appeal, too: The inter app operability is key to get the mind free. iOS does this quite well, superficially. But for me the honey moon phase ended when I realized - well, Stallman was right!
The locked down, and locking-in, overly profit-driven ecosystem just kills it for me.
I believe an ultimate device like that could really revive the Linux desktop, because the device would thrive with a holistic ecosystem, where apps can coexist, don't habe to fight for the user's wallet.
I think at some point they will eventually do it, but why rush it while you’re still raking in money.
I’m suspicious multi-user iPad support is delayed for similar reasons. Many spouses have their own iPad now, when they could probably share if there was multi user support.