But there are some type that would be very usefull...
I don't disagree with you at all: we could absolutely use a whole bunch of new overlays. both small and large. However, that's not what the conversation was about, which was not "what would be good new overlays to have?" but rather "what is the physical format that MMP will use when (or if) they publish the proposed Overlay Pack?".
(The answer, of course, is that they will be published exactly the same way that overlays in ASL have always been published; anyone who thinks otherwise is not only dreaming, they apparently have no prior experience purchasing any ASL products ever.)
All that being said, it's possible I suppose that MMP
will add some new overlays to the Overlay Pack to "sweeten the deal" for people who already own them. Of course, if they do that, there will be the inevitable "I'm being forced to buy something I didn't want to buy" whining. Publishing ASL stuff is inevitably a loser's game; I don't know why anyone bothers.