a very useful request, also something that's available with other slicers..
for e.g. prusa edition of slicer have something called "surface" that's ensuring wall thickness. typical issue - top of the printed busts, balls etc is not perfect.. simplify3d don't have problem with these tops! that this addon solves for slic3r tops problem but the way this is solved in slic3r would be a great addon to simplify3d, it's also how craftware handles steep angles, and it would solve this request of getting "more infill as we move to top", the thing is, it does not change only the infill % for the whole part with Z, it changes the infill % all around the object where infill is close to the wall, so if the wall is slanted you have some dense infill few mm near that wall, same for the top..
also, there was a talk on the forum that I seen, don't remember where, some slicer (maybe also prusa's edition of clic3r or something like that) is offering some "minimal infill" settings, minimal infill that will make the part print ok (so support slanted walls, roofs etc..) ... making something like that and combining it with normal infill ... so a merge of "minimal that would hold the fort" + your regular infill at some % ... would be a super cool feature
then, internal supports. talked about on forum many times .. internal support should help too