I'm CEO at Neon. We are very excited to partner with Microsoft. Happy to answer questions!
If this really is a strategic investment, maybe it means Citus style sharding is on the horizon?
We will consider it in the future. The important property in sharding should be the ability to go up and down in the number of shards. Each shard will increase write throughput and we should allow to go from 1 shard (default) to N to M and back to 1. This way we don't have an "upgrade" problem that Citus has.