I do read all suggestions but right now we don't have time to work on anything which has workarounds. In other words we're prioritising things which are otherwise completely impossible. All three of these can be worked around:
1) Just set up a square collision mask with a bit missing
2) Invisible sprites as 'detectors' has been a standard technique since Classic
3) I don't think the engine really supports this, it's up to you to make your game logic do what you need it to.
So I do appreciate these may be genuinely useful, it's just there are things like Families on the todo list which are making it extremely difficult to make large projects which is quite a severe problem, and these are minor problems in comparison (IMO).