I would expect that the 5G's would be out at least by sometime in the summer, hopefully sooner, but you never know. If you are going to wait, I'd be prepared to wait up to 6 months.
I bought a 4G soon after they came out, so I won't be upgrading anytime soon. I'm hoping the 5G's come with color screens, they just look so much sharper and I wouldn't think the 2" color LCDs would cost too much in mass quanitities that Apple would need. Although, a change like this would probably merge the iPod and iPod photo product lines, so I'm somewhat skeptical that would happen.
I would think an FM tuner might be a possibility as well or line-in/mic recording. People are often requesting those features. Those are not too important to me as I would not use them often.