Well professional developers are often employed by companies that want make use of open source code to sell their proprietary code. It seems more likely to me that those companies will instruct their developers not to work on any GPL code rather than some big ideological shift in the individual developers.
A long time ago I worked on a project which had all the user-facing text strings in their own separate file (for ease of translation). I didn't think much more of it at the time, but even if I was just rubber-stamping this PR then seeing that a code-only refactor was touching the strings file would raise an eyebrow.
I would also like to know! This seems like advice from the early days of Android when the software was way more buggy, everything seems very stable nowadays and I rarely find myself needing to reboot because something is in a bad state.
Same principle as a former burglar who now installs security systems or a former soldier who now works as a bodyguard. You've got the skills, you just want to use them in a different way!
Super Mario Run was quite fun as a single-button Mario platformer. You could also try visual novels or point-and-click adventures, or even something just with simple controls like pokémon.
Well professional developers are often employed by companies that want make use of open source code to sell their proprietary code. It seems more likely to me that those companies will instruct their developers not to work on any GPL code rather than some big ideological shift in the individual developers.