I flew H-46s out in Guam, so I was around when the first fleet MH-60s showed up. For a long time, they were called CH-60, but then somebody up the line somewhere changed it to MH for "multimission," since they'll be doing so much more than just cargo stuff (although 46s did pretty much the same thing the new 60s will do, except for CSAR). When the first batch of 60s got out to Guam, they had "CH-60S" painted on the tail, so that had to be fixed. Now they all say MH, but there's a little square of paint around the M that doesn't match the rest of the airframe.
Also, I don't think the Knighthawk name is official, but it'll probably stick. It's a tribute to the old Seaknight, and since most 60S guys used to fly 46s, they like it. The Air Force has a Nighthawk too, possibly even the MH-60 Nighthawk, and there was some discussion on whether or not we could use the same designation and name, but that never got too far. So it looks like Navy Sierras will be MH-60 Knighthawks for good.
As far as the plan for all helos, it's quite a bit more complicated than just replacing 46s and old 60s (and 53s and 3s and whatever else) with new 60s. There's going to be some major realignment in the helo communities, but I don't think anybody knows what's going to happen for sure yet. Last rumor I heard, HC and HS were going to be combined, and the squadrons would deploy with the carriers, like HS does now, but then send dets out to the CLF ships (and possibly amphibs) like HC does now. I have no idea what they're planning for HSL and HM. Like gatordev said, "who knows"?