Well I am guessing that number 3 will resolve Peter/Harry's relationship, which means that the first three is a loose trilogy around the relationship between Peter/Harry and also MJ.
So if 4,5 and 6, came up with either three decent individual stories, or a trilogy with Peter and a hgue villain, then it could work. I trust Sam Raimi to only do these if he is still interested (and therefore have a better chance of good films).