There should be a way for mid-career devs to do job trades -- like I do your job and you mine (with help from the other person to ramp up kind of like a buddy) for a month or two. It would give companies access to senior talent they could evaluate like internships, and all they would have to do is keep paying the original employee. Even doing this within a big co as an inter-team thing (getting a team rotation or a new team assignment past your first few years) is pretty difficult since your original team is presumably relying on your acquired knowledge.