I have had this concept in mind for a long time, but knew that it's actually impractical. Most of the friction in a cube came from the plactic cubies rubbing against each other, so having a ball bearing at the center piece only reduces a very minor portion of the friction.
However, another idea occured to me some times ago, that if there would be individual rollers on one side of every contacting surface, the turing resistance would be reduced significantly. Similar concept as the tracks on cubes like A2, Alpha mini, Alpha CC, etc. But it then have the problem of stability, which is much harder to solve than having simply raised tracks (which have already been refined significantly now).
BUT, the roller idea may be applied to improve the reverse corner-cutting. Instead of placed at the center of the surface, they could occupy the contacting edges on each pieces, which allows the pieces to glide easier in a misallignment. However, it won't work at certain angles when the pressure is directly perpendicular to the roller; plus, the method of using leverage to overcome the misallignment (i.e. Dayan Guhong) have already proven to be an extremely effective method.
Therefore we may conclude that roller systems on speedcubes are impractical and only adds production cost to the products, raising the already skyrocketed prices of speedcubes now(since when did the Guhone cost $15?)
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