Lots of internal apps at google are written on top of appengine. For example the android developers portal is written on top of it. So i woudnt worry too much.
Good point. But still, it's hard to believe that it's taking years for Google to add to GAE a mature Search API and support for multiple datacenter locations, which are things Google does better than anyone.
Developers outside of Google are not really ready to cope with the daily reality of being inside Google. Things that Google does "easily" like search and multihoming with replication and failover and so forth are actually tremendously difficult. App Engine customers are not willing to embrace the limitations that Google's architecture dictates (indeed, App Engine customers are constantly complaining about the few such very minor limitations to which they are already exposed.)