I can't see any real reason why a lefty shouldn't learn to play a 'right-handed' guitar (as long as it's from scratch). Both hands are busy and arguably, the left hand more so for a 'righty'. Whist it is possible to set up an electronic keyboard to be left-handed, nobody bothers, and leftys can play the piano just as well as rightys.

What is harder is re-learning to play the other way round once you've been playing a while, as the brain's pathways have already been programmed to play the other way round, making it a lot harder to swap.