I am wondering if the new S2 geo indexes are downwards-compatible and can be used with existing data from previous release. Do you see any obstacles for upgrading to 3.4 coming from an older release?
To be on the safe side, it is a good idea to consult the list of incompatible changes/changed behavior before upgrading: https://github.com/arangodb/arangodb/blob/3.4/Documentation/...
That may seem like a huge list at first, but many items on it should actually be minorities.