I think that if FIRST keeps pumping out games with the same relatively flat field with maximum of 30? inclines to climb, you will see more and more 2 speeds. There just isn't a challenge for teams to design anything besides a basic 4"-8" diameter, 4 or 6 wheel drive train. Its related to the arms race thread, but on a broader scale. Most teams wont try to make a V6 or anything like that, but with all the previous designs out there, a 2 speed isn't that much of a stretch for any semi-experienced team.
And there are teams out there that have almost reached perfection as far as 2 speeds go. 254/968 has the most elegant and thought out drive train I have ever seen. And it helps that they have had at least since 2004 to work out their design. I'm not quite sure if you can get any better than a 1.4 pound 2 speed gearbox (great job Travis btw) and I would doubt their entire drive train came out to be over 35 pounds. Thats 85 pounds to do whatever else you want to do with the robot! Being the one who is always working on arms/manipulators, it would be nice to be able to make something without having to worry if the drive train is gonna take up all of the robots weight.
In short, yes, as long as games continue to have fairly repetitive field layouts, 2 speed will become better and popular-er (is that a word?

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Mike C.