It should not be too hard to add support for executing a lambda function pre/post deployment of CDK apps. Basically, a custom resource with a changing logical ID that only reacts to "CREATE" and automatically takes a dependency on everything (or everything takes a dependency on it)

This can be used, for example, to implement "live" integration tests where you deploy a stack and then asserts some things against it at the end of the deployment. If your assertions fail, the stack is rolled backed.