I have a 12.9 and am in the same boat, mainly because of the proccesor alone look at the gains the A11 made for iPhone. Now imagine what the A11X will do. This could also be the first iPad with more ram, based off the direction iOS and MacOS is going 4gb ram isn’t going be suitable for much longer for a “Pro” level iPad Pro. Personally if they don’t add ram I won’t bother upgrading as that is going to be a bottleneck long before the A10X or A11X would be.
iOS can’t start requiring more than 4GN - there are far too many devices in the market with way less ram. I don’t want iOS to suddenly run away with ram requirements - keep it lean. 4GB should be fine for a while yet