So then a competitor can get the Open Source GDrive app, modify it in whatever way they want and prevent Google from making any server side improvements because

So then a competitor can get the Open Source GDrive app, modify it in whatever way they want and prevent Google from making any server side improvements because the OEM's version will become incompatible? Or worst case, the OEM might build their own compatible cloud with their own OEMDrive server that implements their own APIs and fully cuts out Google? Remember Google isn't a charity - they are a business and they have to protect their business interests. Once you start under the incomplete premise of Google with their Open stuff and without their business interests - that's when you start demanding 100% open. IMHO they are as of today doing a fair job balancing both their interests and AOSP's openness. Conflate AOSP and GApps and that's when you get into silly land.