Several comments on the competitive merit of possible types:
Much as the boltbeam combo is hyped, ice/fire actually is nearly as good offensively, due to hitting so many things for 2x and 4x damage, unfortunately with the prevalence of rain it would really only be viable on sun teams :(
Ice/electric and ice/fire are both such terrible defensive typings that even with 680 bsts the new Forms (if they're those types) might well struggle to find usage in ou, being weak to ground fighting and rock, 3 of the most common attacking types in ou.
Fire dragon and elec dragon would obviously be uber, as there wouldn't be a huge difference between them and reshiram/zekrom.
Ice/dragon would be very interesting. As Kyurem showed, phenomenal bst with a poor defensive typing and mediocre offensive movepool is by no means amazing, as the sheer power is not enough to make up for coverage. 680 Bst ice dragons would likely be ou, yet I don't see them being uber, possibly making them the first cover legends not to be uber I believe.
Suicune says hi.
Fire Ice is not that effective offensively and it sucks deffensively. Elec/Ice is really the only viable one if the types turn out to be like that.