If you are trying to go active active.
I'd look at using the new publishing service in the context of Azure SQL (PAAS) to get the web database changes published out to different regions.
(as Azure SQL Geo-Replication is read only in the replicas, and sitecore requires write access to update the properties table)
For the Core database though no equivalent of the new publishing service AFAIK.
Depending what you need out of the Core database, you may be able to get away with having a Core database in each region not kept in sync. (and manually update/keep in sync changes as required)
There is a scaling guide with 3 scenarios I recall, where outside of PAAS you could setup replication (I recall some modifications required to Core databases to support this), which won't work in PAAS.
Or replay security events.
Main issues are keeping security tables in sync.
If your content authors are only in one region, and you don't rely on that for authentication on content delivery, may not need it to be kept in sync.
Other usages of core database are links database.
Storing which is the active solr collection for each index.
Would be good to have a definitive list.
For DR scenario you could have a Geo Replicated core database, and fail over that when you want to fail over content authoring.
Hope that helps.
