Nothing at all. And as we know, they already have released several. Everything so far is 60hz except for Balloon Fight, Kirby's Adventure, and Super Metroid.
The language thing doesn't seem to be an issue either, since Nintendo offers multilingual versions of games for download on the 3DS eShop, such as Link's Awakening. While optional US downloads is perhaps unfair on non-English speakers, a lot of people are stating that they'd rather play in US 60hz than a language they understand (although English is common enough to negate language barriers to an extent), and I'd have to agree. I'd rather have the option of fumbling my way through a 60hz Japanese game than suffering sub-50hz quality.
My guess is that maybe, just maybe, all the promotion games were coded/rated some way back, before the 60hz furore came to light, and all the games coded since were simply lifted from the US store to appease customers. We'll know when the first non-promotion game is (god forbid) 50hz, but if they continue doing this, I don't think it's going to work out too well for them.