The latest iPad Pro IIRC has some sort of post-2 chip (I just don't remember if it's 3 or 3.1), it's just not being used yet. The connector itself has 16 total pins available, and the plug has 8. Since the Type C connector is 18 pins with 2 being orientation detection and 4 being ground, it's still possible to have the Lightning connector itself support 3.1 by actually using both sides at the same time instead of just one at a time; although those extra 2 pins would be handy.
So in terms of the connector itself, they're still pretty comparable, it's just that Apple for whatever reason didn't want to add support for it.
Edit: Cleared up some things that were actually untrue after researching it a bit more.