The nonlegendary section would likely be dominated by Tyrantiar and metagross, metagross because meteor mash and with a second move, having earthquake will hit most all of its defensive counters for big damage (most types that double resist steel are double weak to ground, exceptions being those that are water types; lanturn, empoleon and Rotom wash) and resisting a large number of other pokemon and Tyrantiar because it can counter etagross with bite/crunch-fireblast. while not a pseudo, Gyarados may find a place as a counter to metagross (resisting steel and ground, has neutral water fall and SE crunch). Other pokemon will fall into place as counters to the dominant pokemon, and I have a feeling blissey wont be there, no reasonable DPS and numerous defensive coutners that can outlast it.
Thats just somewhat of a quick prediction/analys, not a definitive nonlegendary PvP guide, as we dont know how the finer points of the mechanics work.
However a lot of legendaries likely wont be too dominant in PvP, most are in raids becaue they have great DPS, but most legendaries, (aside from mewtwo for the most part), have very sizable flaws. moltres, ho-oh, artinuno and rayquaza all have double weaknesses; the regi's are weak to numerous types, most of those weaknesses also resist their STAB; celebi, mew, suicune all deoxys forms when they come out either lack the stats or moves to be effectives; Groudon...oh this one hurts me because its a favoritethough solar beam could add soemthing, frankly ground moves suck; Raikou has a narrow usage (and doesnt benefit from rain generalist status as weathers not in PvP) and is easily walled by ground despite their bad mvoes, entei is also walled by some of its counters (water and rock) the lati's large number of weaknesses combined with somewhat poor moves, and the last one...oh zapdos, as an instinct player this also hurts, Bad moves, mono type set, easily walled by and weak to ground types with secondary types that coutner flying (Rock/ground or ice/ground types)
the dominant ones will likely be Kyogre for blizzard and Thunder both having good coverage (blizzard for grass and solar beam groudon though hydropump counters this too, and thunder for other kyogre)mewtwo for shadow balls/FB combo or any of its other move combos
