I just received my new eRX from 80 Designer Store. The new shifter ergonomic is such an improvement, in my opinion. It's actually heavier than the old eR9 by almost 15gr for each shifter. I'll take the 15gr penalty for improved comfort. Kind of curious how the new eR9 would weigh compared to the new eRX. It seems like an odd choice if eR9 ends up being lighter than the eRX.
I can confirm that the new shifter can be paired with my other eR9 RD and FD. It's funny I can pair two different sets of shifter for one RD and FD, at the same time.