Not sure about this "all new games being doomed on the DSX" thing. I "arm7-fixed" Pokemon platinum and the Wi-fi works great. Actually I have a bunch of "new" (arm7 patched) games with working wi-fi. It seems to be a case of choosing the right arm7.bin file or something. I also noticed that results varies depending on the patching tool used. Some didn't work when using the "patient-donor folders" method but worked when using the "arm7fixa" method where you just drop the rom on the "arm7fixa" program icon and it creates a "ROM-arm7fixed.nds" copy in the same folder. Sometimes it's the other way around.
One thing I can tell you though: *all* the roms I have tried works when patched with the Mariokart arm7.bin. By "works" I don't mean "wi-fi works", I mean "It boots, It saves and it's playable". Trust me, I just bought my dsx from a friend and for the last two weeks I've been going through the 3500 roms (well, those that somewhat interest me,right?) trying them, patching them and whatnot and only 2 roms don't work. Rune factory 2 (white screen) and galaxy wars,although I just read yesterday on this forum that if you auto-boot on the cart it works. So make that ONE rom that doesn't work. I have a folder here with (as of now) 250 roms and they all boots, saves and are playable.
Anyhoooo, the fact that pokemon platinum wi-fi works leads me to think that there *is* a way to make them all work.We just need to find the right method.