While I wouldn't buy a set someone just asked me about highway bars for a Legend.
These are my thoughts on what highway bars should do:
1. Make them more stylish than the competition. I have always like bars set up like these:
http://www.nopork.com/imagesprod/604-1.jpg
They just look more attractive and interesting than the oval ones, or god forbid those awful ones that just dangle from the upper mount with that massive piece of metal. Working the rubber orings into it also lends a touch of class over straight metal ones.
2. Don't limit lean angle.
Shaped like that the bike will be able to lean over far further than the standard oval ones. It would be awesome if you made a hinge that could bend back a little in case of aggressive lean, but under impact would stay put.
3. Weather protection.
Some bars I've seen on Harleys allow you to fit weather protection which is nice considering that with your feet forward both cold and rain is going up your pant leg. You don't even have to develop it right away, just allow for it in you design.
4. I would suggest a rear set of bars, but considering how many different pipe positions there are that's probably going to be hard.
5. Some kind of pad or covering for the part of the bar that will touch down in a simple parking lot tip-over.
That's it. I look forward to seeing this project as it develops.