How to set up a parallel map database
Ideally find an existing good example of project doing this, get them to write Howto and promote it.
OpenMetaMap looks like a past effort in this area
How to fix consistent identifiers
Related to the above, server-side issue for OSM, more policy than technical
See Overpass_API/Permanent_ID for a potential solution
How to model competing boundaries
Current edit activity going on in Kosovo, Montenegro OSMF policy docs say "in future we'll handle this" https://github.com/twain47/Nominatim/issues/202
How to implement geographic locking
We must expect major edit wars at some time in the future - where people create lots of accounts in an automated fashion to edit back and forth a certain area. If that were to happen, it would be good to have a way to temporarily suspend all editing in certain areas (currently the API only has a global read-only flag that the administrators can set but not a local one).
Technically, this could be perhaps implemented by hooking into the changeset area function. The API contains code that, with every edit you make, the bounding box of your current changeset is expanded to cover that edit. It is conceivable to simply throw an exception when an attempt is made to expand a changeset into a "blocked area", thereby suppressing edit activity in that area. (Side effect - global edits that accidentally contain the prohibited area could be affected.)