Edwin, since you're asking: I have been using selections by category for a while now in Dynamo. Zach is right, it's just a bit of Python.
I just shared my category-related nodes as a package called "Select By Category". It doesn't have all the revit categories, just the ones I had needed so far, but I added a node that lists all the available categories, so it would be easy to make new ones. I will keep this in the package manager until there are built-in nodes for this.
Since this has been one of my secret wishes for some time, I also created an issue on GitHub.