What about over-qualified engineers with various skills? What trining should they get, how to hide their experience?
One addressed these things differently at an individual and at the aggregate level. There is no problem of this kind at the aggregate level.
You comment seems to confound education and skills. If one has reasonable education, one can move to an adjacent field if particular skill becomes unnecessary.
There is continuing education through workshops, minicourses, and courses in universities that are within the field of specialization. One also improves his job-retention chances by taking a foreing language, computer skills, etc. Last but should've been mentioned first is management courses and knowlege in general.