This is terrible, possibly toxic advice. Software devs are people too. They burn out, take time off to travel, reflect, take care of family, or just down on their luck being unemployed.

The only advice I'd consider paramount is to take stock of themselves financially and mentally, to assure themselves that they can take on the chaos and uncertainty that follows.

Honestly, if someone showed up with a gap in their resume and claimed that they were doing start-up, open source, etc. for an interview, I'd dig deep into that hard. The open source contribution/project would have to have a sufficiently high bar for it to be even considered. Else, I'd just assume they were being less than honest. I'd rather someone tell me they spent a year working on themselves, playing video games, hiking, etc.