Hmmm I've been considering the same thing lately... Especially since the display is about the only annoyance I have.
The biggest issue I see would probably be finding a display with a compatible controller chip (I'm assuming the LCD has a controller chip on board, but since I haven't disassembled my Rio Receiver I can't be certain on that), Sounds like it's time to do some investigating when I get home tonight
One other issue might be differeing voltage requirements between the LCD and VFD, but even that can be worked around... Honestly even a different controller could probably be worked around with some help from the Linux guys out there...
By the way, is it the NAGP1091AA part that you were looking t?