I think software development is probably relatively easier to slide into than deciding you really want to become a mechanical or chemical engineer. As you say, it's something you can potentially do a bit on the side.

That said, per another comment, as long as the pay is ridiculously good--which odds are it won't actually be by starting over with a tech company--waiting it out and avoiding lifestyle inflation isn't the worst plan. One of my classmates in school retired from investment banking in his 40s and travels and teaches a bit on the side.