Vitess is pretty close to magic for a lot of use cases. The downside of its rebalancer is that the re-sharding process requires a full expansion of the shards that are being re-balanced, which is to say if you have two shards [-80] and [80-], and you want to split out part of the first shard you need to provision two new shards [-40] and [40-80], let the data copy into them, and then you can mark them as active and delete the old [-80] shard. In this brave new cloud world, that not as much of an issue as it would have been in the old data of your own datacenter.

The big problem everyone I have talked to about sharding runs into is managing the shards as you expand. In this case it looks like notion over sharded so they can spin out up to 480 physical nodes, but when they need the 481 it is going to be a nightmare, thats what Vitess gets you for free, expand to any number of shards and just never worry about it again