I recently replaced the 40x2 lcd's in my Midibox SEQ4 with OLEDs from Raystar. These OLEDs are drop-in replacements for standard lcds and work perfectly with the midibox platform. I think they look incredible. The power savings is nice as well.
One important note is that if you are using the Heidenreich case, you will need to have a section of the top curved bar milled out by a machine shop to accommodate the OLEDs. The vertical width of the displays are noticeably longer than standard lcds and the display pcb will interfere with the bar if a section isn't cut out.