I still think that every system should allow for maintenance windows, but I understand not wanting them. Facebook, Google, etc. don’t do maintenance windows, and Dgraph is pitched as a backend solution that should have been used by Google, but they passed on it.
I think the big kicker still is that the data files are part of the upgrade as well and cannot just be dumped between versions. I would think that eventually the data files would not need to be changed between versions just upgrading the algorithms to query/mutate the data in them more efficiently and with more tools/functions.