Don't Wait for Significant Design Changes
The new iPads are still in the development stage which means anything can happen. That said, given the significant changes Apple made to the iPad Pro's design language last year, we'd be surprised if the company overhauled the design in 2020.
You can expect some tweaks, but expect the next version of the iPad Pro to look a lot like last year's models. In other words, don't expect a home button.
That said, you should expect Face ID and the huge edge-to-edge displays that've made the new iPad Pro models so popular.
If you aren't in love with Apple's current design language, you might want to start looking for another tablet.