A unreported zero day is a de facto backdoor. The chain you mentioned has similar flaws as the current strategy. Step 3 would be incredibly difficult. It would be similar to detecting a virus signature, which are easily circumvented. The second party can use trivial techniques to change the signature in a way that makes it incredibly difficult to detect.
Many 0-days are built of of multiple bugs. A triple letter may use bug #1 and bug #2 to get a result, but another party will use bug #1 and bug #3 to get a similar result. Back to square one with corporate/government/personal equipment getting hacked reducing overall security.
Many 0-days are built of of multiple bugs. A triple letter may use bug #1 and bug #2 to get a result, but another party will use bug #1 and bug #3 to get a similar result. Back to square one with corporate/government/personal equipment getting hacked reducing overall security.