The daily digest email is an interesting suggestion. My only concern is people considering that a push notification. Originally, the stance on no push notifications was to encourage people to communicate with people they actually care about and not just communicate with people notifications are telling them to communicate with. It's a nice low pressure system not intended for anything critically important that needs to be delivered right this second. (My girlfriend and I have threads for vacations, but we also have simple grocery lists, etc. Oh, you can also create threads with yourself. So it's kind of like journaling with friends. Or scrapbooking. Messaging is a side effect possibly.
Email digest could be cool. Thanks for your input and your time! Much appreciated