I recently ordered a Mediator 4000Di but it has not arrived yet.
The missing video slot did not bother me too much. Most video slot scandoublers don't work properly with the 4000's AGA or they don't fit the case properly. I had a Amber in my 4000 for a bit. Find an external or internal scandoubler instead. It's not even a problem with the OS 3.9 bb2 rom update that allows vga output during early startup.
If you have a Picasso IV w. SD,you'll probably moving to a cheaper PCI video card anyway. It only eliminates use of the Video toaster and older cards (Opal, IV24) that use the video slot.