Isn't that the whole idea behind RDM? Most DIY lighting devices don't support it now, but many can with a firmware upgrade. I know the dongle doesn't support it (the Enttec PRO does, and the RPM one could with new firmware). Not sure about the Lynx Express. When I do my own designs, I always wire up the transmit and direction pins on the '485 just in case I would want to add RDM down the road. As for unit ID, you could always have some way of programming that in (just like the start address) or add a serial number ROM to each board.
/mike