I agree with Sander. They won't get a good timeslot on any worthwhile stage IMO. If they do get main stage then it will be early on in the day where people will either be waking up or filtering into the festival, plus they will get only about 40-50 minutes. If they do get a good timeslot on a small stage at night then they will face competition from very established bands such as Radiohead or someone of that stature. A lot of bands are releasing new albums this year and will be looking to secure a slot at festivals such as Lollapalooza and All Points West. Expect Beastie Boys, Sigur Rós, Arcade Fire to be a few names that will hope to play on a headlining slot. Also Green Day and blink-182 are back on the circuit this year and are heavily rumoured, and finally reunited bands such as Pavement (who will draw large crowds due to their independent reputation) and Soundgarden will be considered.
The promoters generally look for a mix of pitchfork media inspired independent acts (such as Animal Collective), fairly well known Alternative rock bands and finally massive headlining acts such Bowie
, Muse and Radiohead, and unfortunately X Japan doesn't fall into any of those categories. X wouldn't really suit playing the small tents which showcase dance/hip-hop acts.
They should do small theatres within big venues such as MGS which holds about 5000 people. We're not entirely sure of the level of interest yet so they shouldn't do festivals or really large venues, why not test the consumer market first instead of risking so much by playing in a 13,000+ venue. There are other factors to take into consideration but I don't want to sound really pessimistic about this, I just don't want them to rush things and ultimately backfire thus causing more frustrations for both the fans and the band.
ps - If Yoshiki got bottled he would most definitely cut the set and walk off stage.