I wish there was something similar for SQL Server.
I believe this project was accelerated by having access to the actual SQL parser, the source code of both ends of the wire protocol, and (if necessary) the source of the engine. SQL Server is starting out underwater on a lot of those measures
That said, you probably aren't the first person to ask; so are there similar projects that don't meet all of your criteria or you've not seen anything in that space?
Haven't explored
Then hurray, your project could be out there just waiting for you to meet it! https://github.com/topics/sqlserver https://gitlab.com/explore/projects/topics/sqlserver
On top of not having source concerns, licensing makes sharding less useful. MSSQL on Linux exists but it comes with a bunch of caveats so most people will stick with Windows. Therefore, each instance of the server will MIGHT be Windows License (depending on various factors) + SQL Server licensing and that licensing is not cheap, therefore, with MSSQL, if at all possible, scaling up and not horizontally is generally preferred. You do have Availability groups if Write Primary + Read Only Secondaries work for you.
Also, MSSQL is clearly on maintenance mode. Microsoft continues to support it and sale it because $$$$ but it's not a focus.