Hi @lilostitch96, welcome to the community.
As you see the functionality has been merged, but the API to expose the functionality in Streamlit has not been implemented, so you can’t access it. This is tracked in another issue
FileUploader is going through an overhaul right now, which is why the feature is not public yet. The target date for it and multiple file upload for this is early Q4 (@karriebear don’t hesitate to chime in for additional info !)
While it’s nice to follow Streamlit’s progress through the Github Feature requests and Pull requests, the official way to follow which features are integrated in each Streamlit release is the changelog file 
keep track of this one and you’ll eventually see the new FileUploader !
Fanilo