Keeping in mind that RAM is not one of the things that Apple promotes/reveals it is not possible that they will provide an upgrade to the 9.7 Pro that consists solely of a RAM upgrade.
The 9.7 Pro was released 3/2016 (approx. 18 months after the 9.7 Air 2) The mini 4 was released nearly 2 years after the mini 2. (The mini 3 was purely a cosmetic release)
Since Apple has said repeatedly that customers don't replace their iPads as frequently as they used to, it seems that they've moved beyond the 12 month release cycle to an 18 month cycle or longer.
I expect the 9.7 Pro (internals) to be updated no sooner than 9/2017 though the introduction of a jade gold model could appear in 3/2017. Unless there is some new capabilities introduced into iOS that would require 4GB, I don't believe such an upgrade would include 4GB RAM.
The 12.9 Pro was released in 11/2015 with an additional storage option available 3/2016. I would be surprised to see the 12.9 Pro updated in 2016. I'm betting on a 3/2017 for the 2nd gen 12.9 Pro.