I don't think it's much of a stretch to say that while you can't say the mecanum as a drive system is dead on arrival, it seems to be invariably used by teams who are "in too deep" and would have more than likely struck gold with a 6-wheel tank instead of mining for limestone.
One time mecanum user, first time caller: never again. There were some minor maintenance kerfuffles at Alamo this year with an experimental drive train* but it pales in comparison to the constant retooling of the mecanum wheels and code to get the dadgum thing to drive 4 years ago. Finalist trophy, tell the haters to buzz off and whatever, not worth.
15 years later and we're finding plenty of fun ways to retool the 6WD in new and exciting ways to tailor our team. If you want to drive a mecanum, your call. You want to change drive train design on your team from the ground up annually or bi-annually? Ok.
If it a) goes out and executes a valid strategy and b) an alliance captain sees your valid strategy meshing well with theirs, then there's no reason to not do it.
The fact still remains that seeing a well-executed strategy being driven on 4 mecanum wheels isn't something that comes up too often in the history of FRC, and smart people in FRC love their FRC history. If you want to do a case study on wildly successful mecanum drives, go check out the fantasy section of the library because it's as wild a tale as Dean Kamen in a tux (
well, not that wild).
*(but Wil, why did your team run an experimental drive train at an official FRC regional?
GREAT QUESTION!)