Hello,
First, I wanted to show some appreciation for the new Joined View Layers in ArcGIS Online. They are much more useful and easier (and free!) compared to the previous way of joining data through the analysis tools.
However, one improvement I would want to make to them would be the ability to apply to a filter to the Joined View Layer like you are able to apply to a regular View Layer.
In web maps, of course you can still filter the data but our office uses an asset management system where it brings in services directly so we currently have no way consuming a filtered Joined View Layer. If this option was available, we would get much greater use out of this new feature.
Thanks