App Engine as a single monolithic thing has been broken out into various parts - the datastore is now Firebase (aka Cloud Datastore), the tasks queues are now Cloud Tasks, the blobstore is now Google Cloud Storage, the logging system is now Stackdriver. The thing now called App Engine is the http-serving runtime, and it looks like that part is now being opensourced.

There are some parts of the old monolithic GAE that have doubtful futures (full text search, image processing) and one part that we can't tell from the outside (memcache, which is slightly different from Cloud Memorystore). But overall it doesn't feel like GAE is being discontinued, just changed.

I've been on GAE since the earliest days and while there have definitely been some ups and some downs, the overall offering is vastly better now.