I think the fact they nerfed CotA gave us the answer to this question. If they thought doing bounties/rifts would be at least comparable with CotA they would have maybe left it alone. Don't expect anything near those 4+ bil exp per hour numbers until people are able to efficiently farm T6 in RoS and that will take a long, long time.
Keep in mind that this 50% community buff is multiplicative so it's actually a huge boost. From what I saw on beta nothing came close to the level of experience some people are getting in CotA now. I had 4.3 bil per hour in my premade group yesterday which is insane number and some people in perfect gear and group setup for CotA can go even higher close to 5 bil. It will be possible to reach those numbers again with godly gear on T6 in RoS as well maybe but it will take months to obtain such gear.
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