it wont support portrait…
2224-by-1668 resolution at 264 pixels per inch (ppi)
vs
2732-by-2048 resolution at 264 pixels per inch (ppi)
the 10.5" is going to be 2x retina, just like the 12.9" (which you can tell by the ppi).
so unless you do non-power-of-2-scaling, that gives you a ppi adjusted resolution of 1112-by-834, which is not enough to do portrait with the current UI design.
the 12.9" ends up with 1366-by-1024, which is enough.
all that said, we are in the middle of a new Roon UI design (no ETA so don’t ask), which unifies phone and tablet/desktop designs, and will allow for portrait on all devices.