Same with the D800, well would be I suppose as they are the same camera with the "E" version having the filter removed.
Maybe there will be an "upscaling" option in the next release
Is this lack of any upsampling normal and might this be a 'work in progress' where an upsampling option will be available in a future ACR updates?
Yes...as far as upsampling already large captures, ACR/LR often does not offer upsamped resolutions in the normal Workflow Options or Export sizes...the odds are you won't need to upsample very often and most often you'll be dowsampling...this is normal with large MP captures...you can always upsample with Image Size in Photoshop.
That's what I suspected, as doing upsampling in PS would provide a very similar result. I can always add a Batch to the Image Processor if I needed to have something right out of ACR.
It's still good to get a confirmation the it's 'as designed'.