Currently shell uses 4 finger gestures but this is inconvenient for large hands and/or small touchpads and is generally harder to use than 3 finger gestures. So clearly, this is a usability issue.
On the other hand, this means that programs can’t use 3finger gestures anymore which well, means they can only really implement 2 finger scrolling gestures which is what Web does for example but this might not always be a usable option and would require work on the gtk-side from what I understand.
Currently the only app I know using 3 finger gestures is Builder. (will update this list if someone mentions another)
What are your thoughts on the matter?