We were just in a 4.6 Earthquake here in the Seattle area. I just tried to get google maps to give me the route for tsunami evacuation and it doesn't have that capability. Why not? Anyone from the maps team here?
I think the most likely explanation is that they never thought of it.
Are there official routes designated by local/state/federal government? If so maybe you could contact the relevant authority and ask them to ask Google to add them.
Google maps often has topical information, eg road closures, so it's obviously dynamic rather than just an online equivalent of a paper map. The technology therefore exists to do what you suggest.
This is a great idea! I didn't think about going to the local governments and asking them to reach out. I will get on this come Monday morning!