Back in 2015, when Apple unveiled the 12.9-inch iPad Pro, Apple SVP Phil Schiller said they ultimately picked the screen size because the width of the device matched the height of the existing 9.7-inch iPad. The 12.9-inch iPad Pro is like having two 9.7-inch screens side by side.
Provost takes this idea and runs with it. The width of a 10.5-inch iPad would match the height of the screen on an iPad mini. The 10.5-inch device would also match the resolution of the 12.9-inch iPad Pro, while having the same pixel density of the iPad mini.
The math works out perfectly. This new 10.5″ iPad would have the exact same resolution as the 12.9″ iPad Pro (2732 x 2048), but the same pixel density of the iPad mini (326 ppi instead of 264 ppi). Crunch the numbers, do a little Pythagorean Theorem, and you end up with a screen 10.5″ diagonal (10.47″ to be precise, but none of Apple’s stated screen sizes are exact). In terms of physcial dimensions, the width of this 10.5″ screen would be exactly the same as the height of the iPad mini screen.
While it’s not confirmed, Provost makes a compelling argument for a 10.5-inch iPad. However, it would make more sense for Apple to drop the 9.7-inch iPad form factor in favor of the 10.5-inch, while retaining the iPad mini and 12.9-inch iPad Pro form factors.