I take "HUD" here to just mean "in your line of vision" or "in the context of your actual task" or minimizing any context switch to another interaction (chat window).

Rather I think most implementations of HUD AI interactions so far have been quite poor because the interaction model itself is perhaps immature and no one has quite hit the sweet spot yet (that I know of). Tab autocompletion is a simple gesture, but trades off too much control for more complex scenarios and is too easy to accidentally activate. Inline chat is still a context switch and also not quite right.