Yeah, I understand how you feel, but I mean, pretty much every single challenge that people have thought of (that i've seen approved) can work on any generation, so why not make it available in all of them? Apparently, its some big deal if you have enough patience to beat one of every game doing the challenge (I still fail to see how, its really not that bad.)
There are a couple challenges (you're favorite challenge mainly) that aren't ulti-applicable, and for a good reason. I just don't really see the point in making a challenge RSE exclusive just because you like the generation better. I feel that the whole reason that anyone would post a challenge in the first place is so that they can show others "hey, Pokemon is fun if you only do this"
I am sorta surprised that nobody has made a spin-off/hack challenge. I guess some of the spin offs (Stadium and Stadium 2, if they still exist, Colosseum and XD) are too hard to Emulate maybe?