A way for Google to add value would be to distribute transactions efficiently/optimally among my existing accounts. If they know the terms, promotions and limits on my various cards and bank accounts then they can figure out that a particular transaction is most advantageous to me if it goes against Card A since it gets me a lower rate or a cash back or I have more head-room. Looking at transactions over time Google can predict and optimize how my spending gets allocated. I think I'd like that if it was done well.