Google allows that though or do they mean access of Google Play via 3rd party apps?
Not that I am saying it might not be necessary to include Google from the start, sets a good precedence and prevents a future where they might go the Apple route.
Just hope both Google and Apple won't restrict opening up to Japanese market only. But who am I kidding, they will.
I think this means allowing the listing of third party app stores inside the Google Play Store - so you could search for F-Droid in Google Play for example instead of downloading and installing the .apk manually.
You're still putting complete trust into Google by using any android that isn't thoroughly de-googled, built from scratch, and installed on a jailbroken phone. They're integrated on the OS level they can do whatever they want.