We did something just like that for VEX.
I'll try to get some more pictures of it on the VEX bot though, I designed it around November for the VEX, so our team realized we hadn't seen anything like it really in FRC, so they named it the "Kane-O Drivesystem",
We did it so we would have traction, but still be highly maneuverable, and also because it was pretty unique. We had the front omnis powered also to make the turning radius closer to the center rather than being in the middle of the tracks, which was closer to the rear of the robot.
Sorry for it being somewhat low quality, it was a quickie camera-phone picture.
It worked pretty well, surprisingly, it actually won in a pushing match against another full track design and an articulated track design, (think Scorpion from Halo).
But interesting choice for FRC, I'm interested in seeing how you would modify it for FRC and what advantages it would have over a fulltrack system in real life, compared to VEX scale...or it might just be the same...
Ya never know. lol