What guess game? Last week, the then-current iPad Pro was pretty good, and this week, the new iPad Pro is pretty good.
Last week's will even work with the Magic Keyboard.
Nothing is forcing you to upgrade. Just like with a Mac, an upgrade cycle of three to five years is probably fine.
I have to know whats in the pipeline to make my decision. Apple could go on for another 2 years not releasing a new iPad Pro update or they can release one in early September just 5 months later.