Shaun here, product manager at AppScale Systems. We currently have a number of customers running their applications on AppScale in production (Chico's FAS, the World Wildlife Foundation, and ParknCloud to name a few). We also have quite a few high-profile customers that will be deploying in production in the coming months, so stay tuned :)
Moving to GCP takes a bit of an idealogical shift, but moving off Google is pretty simple if you use AppScale. That might be the best option for these startups; take advantages of the free services from Google and move away after a year if you need to.
That's a good point. I think Google recognizes the value their cloud platform brings to early startups and wants to put their fears to rest about costs (at least the initial $100k).
But startups could easily use AppScale to move off Google and on to AWS/Digital Ocean etc. when they start to get real traction or when the free credits run out.
Customer case studies: http://www.appscale.com/resources/use-cases/