I would be surprised to see full Thunderbolt 3 support on the 2019 model, but it would be nice.I’ve changed my Mind IF there is a 2019 iPad Pro Refresh. Here goes.
#1. Stronger body design less bendy
#2. 6GB RAM across the board
#3. Full featured Thunderbolt 3 port
#4. Tripple Rear Cameras
#5. Included Fast Charger
#6. 8 Core A13X CPU
#7. Bluetooth 5.1 two devices at Once
#8. 128GB base model
#9. HDR10 compliance
But it appears the iPad Pros may already be capable of doing simultaneous USB 3 and 4K 60 Hz even without TB3, although I don't think anyone has confirmed this yet.