[bedatadriven]

I beg to differ. We've run our business on AppEngine for 8+ years. We've never been forced to migrate, and when we've chosen to upgrade to newer runtimes like Java8, the transition was smooth.

Upgrading to Java11 will indeed be a big change, but Java8, with memcache etc, is still very much supported.

[jshen]

I led a team that wrote an app app engine using python 2. When Google upgraded to python 3 they completely rewrote entire libraries, like the one for datastore, so we were forced to either rewrite most of our app or to stay on a deprecated platform that stopped getting new updates.