Browser vendors should show a security warning when encountering this behavior. Default configurations of all software must be to disallow. The burden should be on the enterprise to configure their client devices to allow MITM.
There are already plenty of ways for enterprises to get around this, like having their own CA and deploying that as a trusted CA to their machines. Then they can issue certs that their proxies could use, and their machines would just trust those certs.
Why don't they just use that method?
Also, how would a browser know it has encountered this behavior? A key might be rotated every few minutes, so just seeing the same key twice is not enough; and the key could be derived from a static key and the TLS nonces, so seeing a different key also means nothing.
That said, I think server vendors should not implement this option. It's too risky, since it could be enabled by accident, incompetence, or malice. It's better to force the few who believe they really need this option to implement it themselves.