There's an increasing amount of things you can do with G Suite, almost all our products have APIs and Apps Script libraries.
If there's something missing in our APIs, feel free to let us know.
Almost every single company I've ever seen for 20+ years has open sourced their developer SDK examples. It literally makes no sense what so ever to do anything else.
This has nothing to do with what the OP was talking about which is open sourcing the core app.
You've got to start somewhere. It starts with developer samples, moves into tools, languages (Apps Script), then sub-products.
If you're asking for Google to open source it's products in one big blow, I don't think that will happen without smaller steps. I'm on the team that would probably best start the conversation of considering G Suite in open source. Would love to hear proposals.
Even suggesting that Google Docs, Sheets, and Slides might be open source someday is as unbelievable as suggesting Google's considering open sourcing their search algorithm. But I'd love to be proven wrong.