I saw a podcast where the people were concerned that the lack of ram may impact some of the professional apps being crafted for the 12.9" iPad Pro. That is Apple was marketing the 12.9 as a true replacement for a computer and wanted developers to produce apps accordingly, now they have to deal with less resources.RAM is the ultimate bottleneck
I don't know if that is true, but I can see something running very well on the 12.9" model but not on the smaller version.