Mail-order office furniture vendor Topdeq distributes a variety of desk systems, but its the system called Switch that offers legs with wheels for any of its desktops. They have some interesting shapes as well as desk extensions which are small add on surfaces. Now the picture above is not a mobile desk, but if you look up in the corner the desk behind the partition is fit with the legs with casters.
Here is an enlargement of the image zoomed into the corner with the desk fit out to be mobile. Topdeq is not inexpensive, but they offer fast shipping and a good value compared to the big contract commercial furniture makers.