This is more of out of curiosity, but what happened during the gen 4-5 period of time that changed CAP policies so that customs elements were no longer allowed in cap submissions?
I only occasionally lurked the CAP forums during Gen V and wasn't present around during Gen IV, so I had to dig through PRC and Process Archive to find answers to this, and it seems like it was a combination of different factors. Right at the beginning of BW,
the first post by the TL, reachzero, expressed that he was against the idea of custom elements, as there was so much new stuff to use without having to use them.
A later post during Ability discussion reinforces this position, and also mentions that programming custom elements of Pokemon Online, the main battle simulator at the time, wasn't feasible due to technical issues. Later, during the massive changes to the whole process post-Aurumoth,
this thread put a formal end to custom abilities. I couldn't find anything concrete about moves, but in general, the main reason with Paleo Wave and Shadow Strike exist was because there weren't any good options to use as STABs for those types back then, but after Kitsunoh, that wasn't a problem for other CAPs.
I believe that it also has to do with a cultural shift in CAP. Back in DP, the process was much more relaxed, so adding some custom element wasn't seen as that big of a deal. However, as time passed, CAP began to put more emphasis on utilizing the tools Game Freak has given us to their fullest extent and the process just became much more rigorous, so there wasn't any place left for custom elements that could completely alter the way a CAP works in the middle of the process.
As I said at the beginning, I wasn't around too much back then, so I apologize if I'm misinterpreting some facts here.