it's a very interesting one! I'm not sure if the idea itself really pans out though; would I still be ME if I was born a different sex? Even putting aside obvious genetic differences, I would inevitably have different experiences. Are you still yourself after so much changes? Steins;Gate assumes the answer is yes, so I'll have to jump off from there.
Ruka chose to do it, and if it makes them more comfortable with their body, then I think that's fine. It would erase any struggles they had as a result of their dysphoria, which could be drastic enough to make them a different person, but if they understood and chose that, then I see no problem. Personally I feel that if this application of time travel were real, it would fundamentally change who that person is, so I don't know if I would take the same deal.