I have used the R and A series at the same time, in the same camera. I would imagine there should be no issue using the R or A with E-series.
As for our plans: We've dropped all 16GB or less cards. We've sold all but one of our 32GB Rs. We'll likely continue to rent the 32GB A-series P2 cards and they'll be my first choice in my own work. We'll most likely pick up a few, if not several of the new E-series. The 32GB-E would then be included with camera rentals. The 64 E would be available as an alternative to the 32 A for longer-form shooting, such as concerts and seminiars, etc. where stopping for a re-load is not desired.