I think that the most legitimate angle you've got here is that Gardy is incredibly tough to beat on time - and unfortunately, that angle is the one least likely to result in any action from POP. Timed matches are a necessary evil, and if they acknowledge that Gardy wrecks people with the clock, and ban it as a result, that would be suicide. They would be opening the floodgates for complaints along the lines of "Deck X beats decks Y and Z in thirty-minute swiss, where's the ban?" for years to come. Now I'm not saying that the point isn't a valid one (indeed, I have already agreed to as much), nor am I suggesting that Gardy's thirty minute limit abuse would be the only reason for a ban/restriction/whatever, but you can't really use that angle if it's a ban you're really after.
Even beyond that, though, I don't believe that Gardevoir is unbeatable. You're probably thinking, "Of course not, no deck is unbeatable, genius." But I am confident that, in the sea of ideas that the game's greatest minds have thrown around in an attempt to break the Gardy match wide open, there is a hidden gem that could do it, if only given the opportunity. I saw a couple of neat concepts at Nats that I know are being experimented with right now, and if those don't pan out, more will follow.
The way I'm looking at it right now is this: Gardy is the rough equivalent of Blaze in '04. Same dominating numbers all across the country, same "play it or counter it" mentality. But by the end of that same season, Blaziken had been, in large part, dethroned (Fulop did make it to the finals at Worlds with Blaze, but a lot of focus had shifted to Swampert, Shiftry, Metabyss by that time). I'm thinking that a repeat is possible. And even if Gardy does take Worlds, I will maintain the belief that it wasn't worth the ban. IMO, the only card that has ever warranted a ban is Neo Genesis Slowking, because of the brokenness of the stupid thing, coupled with the unacceptable degree of randomness it forced into the game.
Okay, no more rambling. Bottom line: If there's one thing that's ban-able about Gardy, it's the mirror. But the card itself isn't ban-worthy.