We've looked at that in the past and the time delay caused by logging in at out of Google drive is just too much with the way ios is structured. Plus it doesn't generally function like a simple drive location.
Finally on top of all the storage access complications , most apps dont save as actual files that can be saved to a destination folder, as ios doesn't have a traditional file system. Usually you only get that kind of option with export, and then on ios it frequently is a preset list of destinations like email or airdrop. I haven't seen a open send to so I can't use mega.co or owncloud or others that I would like.
I totally admit I am not an apple expert, just a school technician that has tried to fit teacher/admin needs into establishing inflexible work flows with difficulties .