And then what happened?

They changed a significant charge from CPU time to wall time.

And they did this with an execution model of only giving a single request at a time to a process.

So a process taking half a second to make a query or poll a url is suddenly getting a massive price hike.

Edit: on the other hand a fresh search is suggesting that python 2.7 and with it concurrent requests are coming in a couple months

to be fair the original pricing for app engine was for a google product that was in early beta. Google Docs has been out of beta for a long time, and their storage prices have decreased since they were first released. In addition they have removed file type limitations, and increased max file size to 10gb. It is be beyond unlikely that they would regress and increase prices.