Ever since the news broke that Lucario, Blaziken and Mewtwo were all getting mega evolutions, many people have been getting into a frenzy, claiming that they would cement the first two's place in ubers for a long time, and propel Mewtwo to the top of the food chain in its home metagame. All off the incredibly small amount of info that we have. We still don't know what triggers the transformation beyond holding the appropriate Mega Stone, we still don't know how much the stats will be boosted, we still don't know if these boosts will be uniform across all mega evolutions (safe money is on no, though), you get the idea. Heck, we have no clue how the new Pokémon, the Fairy type and everything else will impact the metagame. And suddenly, we have vastly experienced veterans of the gen 6 metagame popping up everywhere, claiming it's the end of the world.
You know what this reminds me of? That one time, a few days before D/P's Japanese release, when we found out Magneton, Rhydon and Dusclops were all getting evolutions. The outcry was UNANIMOUS. Even I fell for the hype train back then. And you know what happened? Only Magnezone moved on to have a lengthy, successful career. It's still the premier Steel trapper it's always been, and even at the time Magneton felt like the most deserving of an evolution out of the trio. This was due to the fact that Magneton was absolute dead weight when its job (taking out Skarmory) was done, or had no job to do in the first place because the opponent had no Skarmory. But the other two? Nope nope nope. Dusknoir was low OU for the duration of gen 4, before falling to RU (you heard me) this generation AND being leapfrogged by Dusclops since Dusknoir's existence allowed it to use Eviolite. As for Rhyperior, it's been a fixture of the UU metagame for a long time (and a frustrating joke in Conquest)... so much for being as brutally OP as we thought it would be when we first saw it.
So why the wave of panic, exactly? Because Blaziken is already uber? Doesn't mean a whole lot, we've seen ubers instantly demoted to UU or BL just with a new generation coming out. Not that this is likely to happen to Blaziken, but gen 6's brand new environment could screw over a lot of Pokémon, and Blaziken could well be one of them. Heck, if somehow my prayers are heard and we get a perma-weather nerf, Blaziken would unquestionably suffer a great deal, and that mega form could turn out to be the key element that keeps it great.
Or gen 6 could somehow favor something like Blaziken instead, and its stay in ubers could be lengthened by another four years. Who knows? Apparently everyone but me. Hook me up with these time machines, guys. With the tone you're taking, I know you have them.