It's high time we were allowed to use them, as long as encryption isn't involved, of course.
The issue, as I see it, is occupied bandwidth and compatibility with other modes. An Olivia 16-1000 transmission takes up a heck of a lot more bandwidth than CW or even PSK31. I don't know how many times I've been in the middle of a RTTY contact only to get clobbered by an unattended automatic Pactor or Winmor signal. Several years ago, there was a proposal to allow different bandwidths in different parts of the band, but the proposal met with much resistance, probably because of the way it was worded.
As for Pactor 4, the proprietary nature of that mode would seem to exclude it from amateur radio. And, then there's the cost. Approximately $1500 for a proprietary, single-source modem? I don't think so.
The way these modes are used is a valid concern, too. I always thought that amateur radio was a communications medium for radio hobbyists and was specifically not a replacement for other radio services. In my opinion, if the captain of an ocean-going vessel wants to exchange email with folks on the Internet, a satellite-based service would be more appropriate than amateur radio.