If I'm going to park the car for a week, I unplug it because I would think it would produce some sort of drain on the battery.
As for OBD-II compliance, pretty much other things like motorcycles are going that way because the whole system has been around since 1996 and OBD-I even longer. Using something proprietary is not a good idea because you will get many people upset. There's more than OBD-II too. You have to communicate with all of the other systems in the car and that's normally done through the CAN-BUS (which is routed to your OBD-II port). I doubt the Elio would not have that because it's an extremely efficient for all of the systems to talk to each other and since they have Bosch and Teves supplying most of the electronics, there is no way they would ever make anything today that wouldn't have that.
The OBD-II functions and all of the other systems can be routed through a bluetooth or Wi-Fi unit and then to your phone. I know some cars already have it.