Well, according to a Google search, RCI does not really mean anything at all. I guess it is a made up acronym from Sim City, so I was told.
And everyone knows that if it's not found with a Google search, it does not exist.
RCI is an acronym from the SimCity series (like you said) and I think it stands for: Residential, Commercial, and Industrial. In that game, you zone certain areas of the map to specify where people will build houses (R), shops (C), or industries. The RCI are bars that indicate the level of demand to build in each zone in that particular city. If the R bar is high, for example, it means people want to move in and build houses. If you don't have any empty zones left, the bars hint that you may want to zone more in that category. The RCI bar exists in most of the titles in the series, I think, although the only one I've invested significant time playing is SimCity 4. SimCity Societies removed the zoning system, which if I remember correctly was among the main source of ire among the fans. I cannot say for any of the other titles, though, including the latest SimCity: DRM Disaster (that's my nickname for it now).
In this case, I think Arcen expected that a significant number of players would be accustomed to the series, and the term will resonate even if the literal meaning is lost. It obviously didn't work for everyone, though.
*Technically,
all acronyms are made up. If they weren't, there would be no acronyms.