4:58 the arrows of the train signal (top left) are opposite in the both scenes, a small detail that could be missed. And also it shows that when they grew up they walked the opposite way in life unlike when they used to walk in the same direction when they were children.
2023 or 2024, I don't think technology is advanced enough to replace the feeling of handholding or a hug yet, and will take decades for it to be able to do just that. Distance is what kill the love, the longer the distance the faster they grow apart, and the movie is sad because it is realistic.
The ending of the novel: "Takaki thought, "Will she still be there after the train has passed?" as the train continued to rush by. It didn't matter. If it really was her, it was enough of a miracle. He made up his mind. As soon as the train passed, he was going to move on."