I can’t say this comes as a complete surprise, but I think there is one point that needs to be made very clearly: Wave’s idea of a centralized repository for emails is absolutely brilliant, and I am pretty sure that the concept will resurface again and again until a company finally makes it work.
Take your inbox, pick a conversation with several messages in it and take a look at all the repetition of text and quoted lines that it contains. The fact that all this information is scattered across dozens of inboxes, munged, edited, re-re-re-quoted everywhere is terrible.
The idea of storing each email with a unique id in a centralized server and have each conversation create new objects in that database seems like the only way to make email scale hundred fold, as will be necessary in twenty years.
Put this on top of a distributed system such as Git to get the benefits of both locality and remoteness and you have the beginning of a system that looks much better designed than today’s email is.