Thanks for the inquiry. However it's not currently our intention to design camera specific plates for the D5200 and without one in house to perform tests I wouldn't be able to guarantee a fit of the D5100 plate on the newer model. All indications are the body has changed enough the D5100 L-Plate wouldn't be an appropriate fit.
If you send me pictures of the bottom and side profiles of the D5200 lined up next to a metric ruler I'm sure we could find a conventional plate that would mount (no L-Plate, though).
This is why I try to buy my cameras as they are coming out with new models. Buying the older model saves money as they will lower the price to get rid of inventory and make room for the new model. Plus, since the camera one is buying has been on the market a bit, the aftermarket companies already have out their gear for these models.
I love RRS L-Plates so much that I would not even buy a camera that had no L-Plate option. I have one for both my D200 & D5100 bodies.
They may say they have no plans but if the camera sells well and they feel they can make some money, there's no doubt in my mind that they would come out with a version for the D5200 eventually.
The Sunwafoto DLP-04 fits the D5200 pretty well. It was designed for the D7100. I suppose a D7100 plate might still work as the D5200 is about the same thickness plus has multipe slots to set the 1/4 inch bottom screw.
The only issue with I have is that it blocks the door with all your connectors. If I move the camera to the farthest slot it will allow a tight fit for a shutter release or other cable in portrait mode with the door open. The molded straight connector on a shutter or tether cable is tight to make a 90 degree bend out the side - BUT it can be done.
When the camera is installed to the plate there is a back porch lip that will prevent twist. It's made out of nice metal like you would really love. In landscape mode it is GREAT! It works in portrait too but with the above issue that could be better. The really nice plates don't get made for the D5200 but then they cost $90 more.
I've looked high and low and never found anything. On a risk I tried this one - it works. Even better it is WAY cheaper the RRS plates and I like those. I also have the rotator / indexer they make as well. They have some really very nice Pano kit too. They machine nice metal and it is worth a look.