So very preliminary experience with # says this is not something that very many people will be willing to use.

Even before I contact the kids to ask one of them to join me as a guinea pig, I installed the Session software on on # tablet and one # tablet. I launched the iOS app, created an ID, flipped over to the "link a device" QR code, clicked "Link to an existing account" on Android. Result: in 0 out of 4 attempts did the Android version perceive that authorization was granted on the iOS side, even after sitting for a few minutes. Nope. People are not going to fiddle with it to try to get one ID active on two devices. (Incidentally, two devices connected to the same ID is the maximum allowed. If you have two phones and two tablets, you won't be able to use the same ID on all of them.)