I've been working on this one for a while since the letters came out on this.
The deal is that in most of the metro areas of the US Kingdom Halls are very overloaded and the RBCs are very far behind in building new Halls. They seem to do OK with remodels but the new projects can take years and years. Based on everything I've been able to determine, it looks like the way the RBCs work may change, since the direction is to take the way construction works in other countries (where groups of full-time construction servants do all the projects) and the way RBC has worked in the US and that the two operating models will be fused together somehow.
The folks I talked to seemed to think that it was a possibility that the RBC organizations in whatever their new form will be would help with organizing local volunteer help and would operate in more rural areas where there is not as much of a need for new KHs - these RBCs are not as far behind as some of the ones in the US metro areas. It looks like those would come under direction of the new Local Design/Construction department at the branch office. The metro areas where the need is greatest would probably have LDC field offices that the guys who used to be RBC would report in to. It sounds like full time branch appointees would be in oversight - not so much local folks who can't work full time during the week.
The main idea here is that work has to go on during the week - seven days a week - and not just on the weekends. This is the main impetus behind the change as I understand it from the folks I talked with.