They added some preview support for CosmosDB recently to Azure Storage Explorer. https://azure.microsoft.com/en-us/features/storage-explorer/

But I haven't used it with CosmosDB yet.

It seems like that's the direction they're taking. But there is a lot of SSMS functionality I can't do without (replication, sql agent, RedGate SQL Prompt!, etc). This is a good start, but still a ways from a solid DBA tool. Pretty dashboard, so maybe I can keep it on a 3rd monitor but do all the heavy lifting in SSMS.

I think there's a VS Code plugin for CosmosDB.

I think so. It’s based on a fork of Visual Studio Code.