A lot of people miss Cata and would gladly go back but sadly the Wotlk cow still has milk in it. Back before the Molten database was stolen Cata was quite popular (prior to the MOP launch) but after they relaunched as Warmane they launched all expansions at the same time and Cata faded in the background. If they relaunch a Cata server now though it will gain a lot of popularity simply because it's new. I doubt that we will see that happen though.