I tried the changes on PTR for a bit and I am wholly unimpressed. Choosing between Eradication and RE just sucks. We have, as a community, railed against long cast time Chaos Bolt since the start of the Mists revamp that brought it's current iteration and they just keep on trying to drag it back up and introducing it in new and interesting ways, and every time they do the community moans cause long cast times suck in both PvE and PvP.
When your community consistently chooses the option to have a shorter cast time on Chaos Bolt, even when theory crafters and sims prove that they get more damage by choosing the longer cast, it should tell you something about how they feel. The WoW community rarely if ever chooses the option to do less damage, so when we do, it's cause of significant reasons.