what are the advantages of a MLS over a GPS
You can cook a TV dinner on the approach with an MLS - but you'd better not have to go around or it might get overdone.
Sorry I don't have any real answers, but I think at least part of airplane design is still marketing. Some prospective buyers are used to seeing certain configurations and would be worried by radical designs, whereas others are looking specifically for such things.
I've seen a 182 with canards and it looked really odd.