Generating the config during deployment, eh... often necessary. Best done with transforms and templates because they're simple.

Executable config, run during startup or, worse, on each request? NO.

[edit] I think that's the main disconnect here: 'past compile time'. The whole point of testing, strong type systems, etc is to lock down the set of states the system can be in. If your configuration is so 'dynamic' you are essentially abandoning all those benefits and saying 'yeah, do what you like to our live servers'.

In short, configuration which is that powerful is indistinguishable from running untested code in production.