Next iPads could do with 2 USB C ports! I think it's better than it was with the iPhone where you would need one set for the phone, and another for your mac or anything else (now you need one set for your iPhone and one set for your iPad, and if yo don't have a USB C mac then another set for that). The 3.5mm jack became a universal standard for a reason! considering the latest iPhones are no smaller than the 6s, and certainly no smaller than the 5s, I don't think the 'we need the space for other things' argument is very credible. And certainly not for much larger iPads.
I have been wireless for a while now and can’t imagine ever using wired headphones again, but I can see how frustrating it would be for those who need or want wired audio devices (especially in a ‘Pro’ iPad). And I am not sure why they just didn’t leave the jack in the new iPad pros since it appears to be thick enough to accommodate it, as this as it is.