Sure, but this approach is going to be much more complicated and less predictable than the "switch the docroot to a completely different directory" model. (e.g. you need to distinguish between asset and non-asset directories, and make a decision about how long to keep "old" assets around.) With some effort these problems can be solved, I'm just pointing out that even with a completely static site, and perfectly atomic docroot switching, you can still end up with clients in an inconsistent state.