Selection tool seems to be a popular topic in the feature request forums, but I didn't find anyone complaining about exactly the same thing I am going to suggest.
If I want to select a bunch of points with the Direct selection tool I usually drag a marquee to start selecting, but often am not able to select all the points I want in one move, so I have to shift drag to select additional points. This is when the annyoing thing happens. Points that are previously selected becomes deselected if I drag over them again, while points that where not selected becomes selected. This is confusing and feels quite messy. The inconsistency I am talking about happens when I use the lasso tool instead. Now I can deselect with Alt and add to selection with Shift (good behaviour!) This is also the way it works in Photoshop.
Shift select to add, alt select to deselect! This should be the behaviour for all selection tools in all Adobe programs! It would be much more consistent with Photoshop as well. Right now using the alt-modifier with the Direct selection tool gives you the group select tool instead, so that would have to change. Maybe you can add an option for this old behavour in preferences for lecacy reasons...
If this option is somehow possible allready then I might be missing something, but I didn't find anything like that in preferences.