While Ruby is nice in a lot of ways, there is absolutely no plan of making Ruby an equal with Python in the ArcGIS stack. It would occupy the exact same space in the ArcGIS system, meaning there are two competing solutions to the exact same problem. We've put quite a bit of effort into improving the Python APIs over the last few versions to make them feel more native, and not just the old Dispatch way of handling things. To do so on Ruby as well would make scripting downright scizophrenic: making a clean Ruby API is a totally different set of motivating factors when compared to a Python API, so not only would arcpy and its Ruby equivalent be independent implementations and designs of one another, but knowing one would in no way imply that you could translate it to the other. And most importantly, Ruby lacks the interoperability and scientific computing backing that Python does: for instance, NumPy and the related buffer protocol for exchanging binary data do not have direct Ruby equivalents.