Sure, for little things like typing a long email. But for most serious uses you should still get a laptop. I’ve seen more than a few cases of people going through multiple Magic Keyboards Because they try to do too much with it.
Why? An iPad Pro is superior to a MacBook Pro and Air because it has better hardware and touch screen support.
And if you do more “serious uses” like music production, with touch support you can actually touch all the knobs and sliders, rather than moving them with a mouse, which is less intuitive. You can probably even play the instruments with the touch screen rather than using an external midi keyboard if you are on the go.
If Apple actually opens up the iPad Pro to OS X, the 13” MBA and 13” MBP are dead basically.
But that is the reason why Apple will never “unleash” the iPad Pro as it would hurt the MAC sales.