Hi @iain, for the 1st item, try using qgrid via shinywidgets:
Currently we don't have "1st class" solutions for the other 2 items, but it doesn't seem like porting relevant projects over to python would be very difficult.
Thanks @cpsievert, qgrid looks like a great alternative to DT based on the demo app in the third link you shared.
Regarding shiny validate, I can't speak highly enough about how impactful this package has been at improving the UX of the apps that I build at my company. It is the type of feedback interaction every user expects of an app.