Better GPS systems that support Galileo and have built-in sensors (e.g. accelerometers) to cover areas where you have no or bad reception. Bigger screens, but input methods are likely to remain lousy and battery life will suffer. Faster CPU's will speed things up. On-board software will remain a strange mixture of things that work and things that feel like regressions. More memory will allow more of everything to be kept on board. Online capabilities will allow data to be streamed from the internet at a massive battery cost.
What I would LOVE to see is the possibility to add my own "apps" to the GPS, and even integrate them with the existing functionality (i.e. let me write software that draws on the map, is integrated in menu's, etc.). Will any GPS manufacturer be so forward thinking? It will revolutionize some of the problem solving in the field, I can tell you ;-)
At some point I've approached Garmin to ask for extra features in MapSource (because the potential is there for so much more). One of the things I asked for was "open source it" - maybe not everything (map unlocking is likely to be tricky) but those features can be hidden away in libraries. They declined, of course, which is a great shame: a dedicated, capable programmer with an interest in Geocaching could turn it into something much better.