The advantages of the iPad Pro over the iPad Air are:
- Promotion display - smoother scrolling effect
- Liquid Retina display - (very) slightly better contrast in colors
- better multitask processor (but slower single task) - not noticeable for average user
- starts at 128GB storage (versus 64GB storage in the Air)
- better rear camera
- 4 speakers (versus just 2 in the Air)
Arguable: Face ID in the Pro versus Touch ID (on the power button) in the Air. Personally, I have a love/hate relationship with Face ID. For me at least, Face ID doesn't work 100% unless I'm staring at the camera directly, which I'm not always doing with an iPad. And Face ID doesn't allow for more than one saved biometric (ie. can't have your SO or DD/DS face saved). For these reasons, I prefer to have Touch ID.
If you have the extra $200 available, the iPad Pro 11" is better IMO, if you need a new iPad now.
No one knows, but I believe Apple will refresh (probably not a design change, but more like upgraded specs) sometime early 2021.