Meh, I don't see how people can worry about Raikou "dominating" the metagame even if it got the correct nature. Just being able to 2-hko most of the meta IF it manages to hit the switch in with the RIGHT ATTACK, is not very impressive.
Raikou may be on a different level of speed, but the reason why fast sweepers like Azelf, Infernape and Gengar are not truly dominant in the meta is because they cannot win the long-term speed war. Choice Scarf (not to mention priority moves) creates a completely different dimention to the speed war, and without unnaturally high speed (ie. you are boosting yourself or your name is Deoxys-S), purely speed-based sweeping is not really all that viable. These fast sweepers are usually only able to take out 1 enemy poke at best in the early-mid game. Now if your name is Yache-Garchomp (you've got awesome typing and defensive base stats better than swampert's to go along with your high speed), it's a different story. Raikou's got fair defensive stats, but Pure Electric is lacking in resistances needed to help it set up, and bulky grounds (not to mention FLYGON) are completely immune to its main STAB. Fighting coverage certainly deals with the issue Zapdos/Jolteon's always had with Tyranitar, but the issue with ground types goes largely unresolved (especially since you'll be really tempted to tack on shadow ball and calm mind).
Plus, calm mind boosting is really better when you have good DEF to rely on (like Suicune). Suicune is a great calm minder. Latias (and ultimately Raikou too) is a "meh" calm minder, especially with the physical orientation of the meta.
Even if you say that Raikou can be great sweeping late game when the enemy is weakened enough that non-stab neutral attacks can finish stuff off-- the same can be said of almost any offensive pokemon in the game. Looking at things like Flygon and Lucario, Aura Sphere Raikou is nothing extra-ordinary in terms of late game sweeping.
I think Raikou would definitely make its way into OU with Timid Aura Sphere-- but I'd highly doubt it could make it into the top 10 on the usage rank. Definitely not top 5.