I've owned an 09 GS (my best and favorite BMW or others, because of its usable power, handling, comfort and relative ease of maintenance) and I'll be getting another 2012/13 in the next few months. I wish the new WC version were available to test drive so I could do an A/B comparison, but I don't see it that happening. Anyway, I'm sure that the new "WC" will be great in the same way Porsche was when they introduced their WC version (yea, there were a lot old timers like myself who felt it was blasphemy, However, it was a "much" better real world, everyday performer and I bet the new WC-GS will follow suit).
Will accessories from the current GS commingle with the new WC version? I "one reporters opinion" think not (well, maybe certain "soft" luggage systems). Because of that, I betcha numerous aftermarket companies are licking their chops to start developing/producing accessories,however that "might" be cut short if the new WC/GS is so "overall" good/better/improved, causing buyers to not look any further, than BMW's catalog (if ya know what I mean).
To all, have a good day and enjoy your ride!!!!!!!!!!!!!!!!!!