I made an experiment connecting to MongoDB server from web browser and using Change Streams for reactive updates.
The idea is that by allowing web clients to directly connect to a MongoDB database server we remove all the overhead and latency introduced by intermediary code: multiple serializations and deserializations, memory buffers, etc. Because web browsers cannot directly connect to a TCP port, the web app exposes a thin WebSockets-TCP proxy which does not process packets but just passes them back and forth.
Change Streams is an official MongoDB API since MongoDB 3.6 to hook into the oplog and receive a stream of notifications as documents in a collection are being modified.
This web app then uses Vue to render the example reactive collection.
See it here: https://github.com/mitar/web-mongo
Feedback & discussion welcome.