The 10.9" might be for the base iPad in the long run. The iPad is set up as a bit of a hand-me-down chain at the moment, so it wouldn't be surprising for the Air to go to the 11" Pro chassis and the iPad to get the current 10.9" Air chassis, with the only question being what then becomes of the 11" Pro. It sounds like this would be at least a year (probably 2) away with the near term plans for the base iPad. By then the Pro line would be well due a redesign anyway, so you'd in the space of a year see the iPad Pro get a completely new design, the Air go to the the 11" Pro design, and the iPad get the Air 10.9" design.
2021: 10.2" iPad gets a laminated display. iPad Air chip bump(?). iPad pro chip bump/extra miniLED model
2022: 10.2" iPad gets a new chip but no design change. iPad Air gets the 11" Pro design. iPad pro redesign
2023: 10.2" iPad becomes 10.9" iPad, adopting the Air design. iPad Air chip bump(?). iPad Pro chip bump(?)