It's technically possible for us to build that, but we're focusing on the most common requests at this time. If anyone has that please let your account reps know (they feed us lots of great feedback for prioritization), or start a discussion on our Google Group: https://groups.google.com/forum/#!forum/google-cloud-firesto...
Yes, this is what we like about RDS/DynamoDB/CosmosDB. Being able to run low-latency replicas (bonus if they accept writes) is important for distributed apps, but the current multi-region deployment adds too much overhead.