4% is a fairly risky withdrawal rate at such a young age. But also being so young, I'd imagine one or both of them will get the itch to do something that earns more money at some point in the next few decades.
Yeah definitely, from reading the article it sounds like they just want the freedom to do what they want to do (and that likely could come with bonus income). The article mentions the programmer's wife is an optometrist and is still working actually.