I wasn't planning on buying for a couple of years, but IF:
1) iOS got mouse support
2) iOS got proper external storage support
3) All iPad Pro models got at least 6 GB RAM
4) The entry level iPad Pro got 128 GB storage
Then I may buy. I can pass down this 64 GB iPad Pro 10.5" with 4 GB RAM (which I just bought last month actually) to my wife. She passed down her iPad Air 2 to our kids so now she has no iPad at all, and just borrows the kids' iPads when she needs one.
My 64 GB model is OK, but it's a bit tight now that I use it for more stuff than I did with my old iPad. However, I don't want to pay for 256 GB since I don't need it. Also, I don't want to pay big bucks to get the same 4 GB RAM that I have now. 128 GB and 6 GB RAM would be perfect... if I could actually use it fully.