J.M Barrie said that he originally intended for Crichton to marry Lady Mary. How would this kind of ending have had a stronger satirical effect on the play? Do you have any tips or ideas to back up these claims?
Oh my gosh! If Crichton married Lady Mary, that would completely upset the British cup of tea, wouldn't it!? The entire point is that British society is not evolved enough to accept a butler marrying an aristocrat. If Crichton actually married Lady Mary, it would prove the opposite, that British society IS evolved enough to accept marriage in between class lines.
I keep going back to your idea of this having "a stronger satirical effect" if those two were to marry. There IS a way that could be an even heftier satire. For example, perhaps if Crichton married Lady Mary, the aristocrats all would have ganged up on them and sent them back to the tropical island to live out their lives there... because THAT is the only place that could accept such a GHASTLY change in caste. See?
Apart from that idea, though, I think Barrie used the proper ending appropriate for mild satire. This is NOT Swift's "A Modest Proposal." The idea above would be too rash and out of the realm of British reality. Instead, it was appropriate to see a reluctant Crichton and a reluctant Lady Mary resuming their previous roles as butler and aristocrat (as opposed to their leader and peasant roles on the island).