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With CFW you can rom hack and make your own harder versions.
There are already trainer and wild encounter editors for XY and ORAS, people have made difficulty/all Pokemon hacks for them already. The guy behind the Star/Rutile ORAS hack promised a S&M hack too for greater challenge, hopefully he delivers.
GF is retarded, so that's the only way. BW2 Challenge Mode even wasn't hard at all after the first 2 gyms, it needed to do so much more. Just play Blaze Black 2 to get an idea of how it should have been done.