iPad Pro is Apple’s flagship hi-end tablet, with first generation announced in fall 2015. If you want to own hi-end tablet, the iPad Pro is the best solution, because, as for Android, only Samsung is selling Android tablet with hi-end specs. Another problem is, that many of Android apps are not optimized for tablets’ big screen, they are just oversized phone apps. Even Google itself abandoned its tablets. As for tablets with Windows, yes, there is touch interface optimized for fingers, but to be honest, how many touch based apps you may find on Windows platform? For anything more advanced you need desktop mode, so your tablet will become a laptop with touch screen. If you already have computer from Apple, and you want a hi-end tablet, iPad Pro is the best choice. I have also written an article Why I have chosen iPad Pro over Microsoft Surface Pro?.
First refresh of 1st generation of iPad Pro from 2015 (and its 9.7-inch version from March 2016) was on 2017 WWDC in June 2017. For third generation of iPads Pro, we had to wait until October 2018. It looks like Apple upgrades its hi-end iPads every 18 months. And this probably won’t change.
Apple’s CFO Luca Maestri has provided a clue that the iPad Pro probably won’t be refreshed in 2019. On Apple’s earnings call this afternoon Luca Maestri said that Apple’s revenue guidance for the holiday quarter accounts for the fact that the iPad Pro will have different launch timing on a year-over-year basis.
This looks like Apple will refresh iPad Pro line at March 2020 event. There is no official declaring for March 2020 event, but Apple usually hosts event in March.