This is only necessary for single-product companies. Otherwise, just do mandatory career broadening assignments like the military does. You have to learn about and work on many parts of many stacks and regularly change teams and product lines. There is no need to fire people to keep them working in one position forever and building fiefdoms.
Heck, militaries even have interbranch and even international exchange programs. There is no reason in principle companies can't do the same and temporarily trade out employees every now and again to learn how things work elsewhere. It would have to be subject to pretty strict NDAs and limitation of sensitive data access, but given the sensitivity of classified defense data, if the military can make it work, private companies should be able to make it work, too.
That handles the specific problem of people not broadening their skills and I certainly wouldn't say that firing people is the best way to get more perspectives in your company. There's a general question of how to get rid of employees that are entrenched, want to stay, but aren't providing enough value.
Heck, militaries even have interbranch and even international exchange programs. There is no reason in principle companies can't do the same and temporarily trade out employees every now and again to learn how things work elsewhere. It would have to be subject to pretty strict NDAs and limitation of sensitive data access, but given the sensitivity of classified defense data, if the military can make it work, private companies should be able to make it work, too.