After reading about the AIS-2-USB, and my use of a USB GPS, I started wondering if the RS-232 connection will soon be going away. Will radar units, or other marine electronics, start using USB? Will the RS-232 multiplexer be replaced with a USB hub?
NMEA-0183 which is the standard used for most marine electronics dictates an RS-422 interface. It happens that an RS-232 interface works also.
As you note many newer marine devices are offering a USB connector. The way they are able to do that is to integrate a RS-232/422 to USB chipset into their electronics and use driver software that creates a virtual serial port. Two such chipsets/drivers are FTDI and Prolific.
So I don't think RS-232 is going away, but we will see more devices not needing external conversion to USB (i.e. Keyspan adapter, or Shipmodul Multiplexer).