It is hard to say how limited it is. No one knows except Leopold.co.kr and Realforce in Japan. I would like to think that it is limited. Somewhere here or on deskthority that I read it is something specially made between Korean Leopold and Realforce in Japan. I casually searched a few days ago and I didn't see any anniversay edition availabe on the Japanese sites I searched.
The body of the keyboard is the same as the regular 87U except it has red LEDs instead of blue (really not a big deal). The real limited feature at this time is the colors of the keycaps. There are realforce keycap set you can buy, but so far they are single color per set (blue, orange, white, yellow). This anniversary edition has a blue/grey two-tone color combo. It the grand scheme of things it is not that big of a deal. But I would like to think that its resell value would hold up well, especially if it is sold out later.
If you don't already have a Realforce, then I would say buy this. If you already have an 87U or money is tight, then don't get it. Don't over extend :-)