This has probably already been mentioned (and I hope I'm not opening a just-closed can of worms), but I just dug out the VTSC Scout Trooper, the ROTS BARC Trooper pack-in, and the Chronicles: The Prequels book to do a quick rundown of the differences in the armor between the BARCs and the Scout Troopers. I would like to say that as long as the head is changed (and it appears to be from the photos at SDCC), I won't have a problem with this figure at all. Much like Gree, the only thing I really found objectionable was the helmet paint, so there you go. This is for informational purposes only:
Helmet: The BARC's helmet overall is slightly modified, with a larger visor and the angle of the chin portion is not as triangular as the ROTJ scout's chin (the BARC's is more trapezoidal in shape)
Chest Armor: Slight differences, most akin to the differences between the Stormtroopers of the OT having the "blocky" layout and the prequel Clones having a more curved layout in the chest plates
Packs: As mentioned before, the BARCs have more pockets on their midsections, but the overall composition of the waist seems to be very similar.
Codpiece: The BARCs have an actual codpiece along the lines of Jango or Boba Fett's (triangular) whereas the Scout Troopers have that "crotch diaper" looking thing. Again, not a huge difference.
Gloves: The BARCs have the little green "back of the hand" protectors whereas the Scouts just have black gloves.
Thighs: The BARCs have some inner thigh armor that the Scouts don't have (an interesting note is that, at least on mine, the ROTS BARC's thigh armor isn't painted green as it is in the film).
Shins: Where the Biker Scouts have the plain looking white boots, the BARC's boots are textured and seem to have actual armor on them. Also, the BARC has no ankle holster.
Again, this is just what I saw, but like I said, the head seems to be fixed and that's good enough for me.