Just a reminder that, if you critically depend on a IaaS/PaaS/SaaS, you should be able to trivially replace it, sometimes as quickly as overnight. Having the service be completely open source so you can self-host generally helps, as does open protocols and standards. Especially important when it's a Google service given their historical speed of deprecation and abruptness in announcement.
If you can trivially replace it with something else overnight, the SaaS might be a bit too simplistic to use in the first place, no?
I think OP means you should write your interfaces with SaaS such that changing to a different provider is relatively easy (just rewrite a little client code or something to fit the new provider to your abstractions).