Is the true end goal one single shard for all players?
TL;DRA single shard for all players is the ambition but no definite answer is possible; they plan to start with many small shards, reduce to one per region, and need new game mechanics too.
This is our ambition, however giving a definite answer is not possible at this point.
We will start with many small shards per region and slowly reduce the number of shards. The first major goal will be to reduce this to only needing one single shard per region. To get there, our plan is to gradually increase player count per shard and constantly improve the backend and client tech to support more and more players.
It's not just technology changes that are required to get to this goal - new game design and game mechanics are needed too. Without mechanics to prevent every single player going to the same location, a large mega shard will be very hard to achieve, especially on the client. For example, there could be a mechanic to temporarily close jump points to crowded locations, or create new layers for certain locations.
While the backend is designed to scale horizontally, the game client runs on one single machine and is limited to a definite number of CPU/GPU cores as well as memory.
Only once we overcome these hurdles, and accomplish one mega-shard per region, will we be able to take on the final boss: Merging regional shards into one global mega shard.
This comes with its own set of issues, as locality plays a big role in the player experience. For example, latency between services within the same datacenter is much lower than latency between services that are hosted in two regionally-separated datacenters. And while we designed the backend to support one global shard, it is an operational challenge to deploy the backend in a way that doesn't favor one group of players over another.