Having two lines of high voltage charging is very impractical. I'm still hoping Tesla will eventually sell a CCS 1 combo adapter.
I see no reason why the port would have to be on the other side. Model 3/Y flap is large enough to fit two ports - it already does in China I believe. Model S/X flap can be redesigned to be larger whenever they get the exterior refresh. That probably is already planned since they already use dual ports in China. The S there has a gas cap-like door.