Not if sessionID is linked to IP address with short expiration. Yes its not nice, but certainly not impossible, which is the point I am making. Content that require authentication should not be shared by users in form of passing direct URL anyway.
The reason (as I see it) GMail wants cookies is not of technical impossibility to workaround it, but that these cookies are essential for non-session tracking capabilities.
Linking together cookied searches should generate pretty rich data for targeting purposes, but linking these to actual people with valid email addresses is even more important as it will allow to actually run nice targeted campaigns.