First off, if they implement anything like this, it should be optional. Some people prefer putting individual items in HotBars, some don't.
And really, I would hope for a 2 level setup. Similar to what happens if you click the Throw button. You get a single popup with all the things you can throw. And that can get bloated very quickly. I'd prefer a set up popups that are more specific. So you'd have a list of buttons, each of which gave you a popup of the items you can use. A two-level setup.
It's going to depend on whether you can remember all the stuff you have that's actionable. Some people can. Or they have a very specific subset in their HotBars. I'm in the other category. I need to see and evaluate things each time through.
But I agree, anything more than two levels becomes confusing very quickly.
