App Engine without it's services is an archaic and expensive instance scaling service in an age of cloud innovations, totally beats it's core purpose in my opinion, it's not an "App Engine" any more
I guess what I mourn most is my lost experience with App Engine, I had all the gimmicks sorted out, but I guess it should be fun reinventing the wheel, playing with new technologies
Firebase / Firebase DB / it's realtime capabilities, in theory, seemed super fun to me, but having experience with App Engine, what matters is how well you know the service and how it performs in high throughput scenarios, that's why I won't easily abandon App Engine, as I exactly know how it performs, where the limits lie, how to work around them etc.