I'm sure I'll sign up for the new cards for the bonuses, but at the end of the day I'll likely shift all my spend to Chase Sapphire Reserve (and Chase Freedom for the 5x bonus categories). A large portion of my charges are travel and restaurant anyway, and the incremental difference on base spend that I might get from a cash back card likely isn't worth the hassle. Then I'll keep using Amex platinum for airline charges.
I have enough SPG points to cover my airline transfers for the next few years, and other than occasional JAL and Asiana transfers, I've been able to handle my typical international air travel reasonably well using Ultimate Reward points. It will be a little weird because the SPG card has been my go to since the early 2000s, but I don't need the annual night credits anymore since I'll have lifetime platinum anyway, and I'm not sure the other benefits will be worth carrying the card if my spend is going to be minimal.