I wish I had current-day AI (and a big credit card) for my previous job, they had a big legacy mess made by a productive but not very good developer, but my job was to rebuild it.

If I had AI tooling at the time I'd probably be more inclined to have it both refactor / optimize the existing application, add automated regression tests etc, and use it to extract all of the features and requirements for it for a potential rebuild.

But honestly I think if that application was properly designed and factored (instead of nesting JS in HTML in strings in JS or concatenating XML from query results only for it to be converted to JSON taking up 50% of response time) its lifetime could've been extended, especially if it was then containerized into a HHVM or similar php optimizer.

But, hindsight.