I wasn't necessarily saying they have to make a complete career switch but rather find a niche within those fields that can use their software experience. For example, building a pressure systems database that isn't god-awful would be useful for oil/gas or firms that do aerospace research. Knowing the mechanical side would obviously be a huge plus, but it's also possible to lean on the mechanical engineers who are the system experts. Same thing with managing environmental requirements, or building automation/energy systems, data acquisition for medical devices, or software quality testing etc.