I might be Tempted to go for a gravel bike that can run 700x38 and also 650x2.1 mtb and then just having 2 wheelsets. But I don't know........When I jump on a bike I just expect that bike to handle a certain way.
2 wheel sets on one bike is like trying to alternate driving a Toyota Prius and a Ford Crown Victoria back to back. turning head lights off at night because it starts raining. Derp! Nope that wasn't the Wipers lever!