Update: Unfortunately, neither ASUS nor NVIDIA had anything of value to say about this device:
Officially, no comment on unannounced products.
First I have heard of it, especially since the next tablets up on the roadmap are Windows based.
As many readers have already pointed out in the comments, perhaps this will be a Windows RT tablet. Time will tell.
This is a curious one; a mysterious ASUS tablet has shown up out of the blue at the FCC today, with the model name 'TF500T'.