They already essentially did this with Connected Realm clusters. It’s not like there’s tons of players on the other PvE cluster that Mankirk cluster would suddenly absorb if they did merge them or cluster them. Same with the PvP side.
The reality is that 99% of the Era players are already on Whitemane and Mankirk clusters today. Anyone who isn’t has a Free Character Move to transfer them to Whitemane and Mankirk.
I don’t think that merging or clustering further will have the outcome people think it will.