I have been this entire time, even since the beginning of development.
Also, there are no speed advantages, or anything to using a certain region of the game. The frame rate, ect is the same across all regions.
DS doesn't even have any region lock. Honestly the EU, and US versions are merely ROM hacks of the JP version, since they're all so similar.
As a matter of fact, the only reason that I have to use the EU version is because that's the version of the game most ASM hacks are made for, and that's only because the people that make them happen to live in the regions where that version was sold.
Plus there's not any slow down, I test on real hardware all the time, and if I put the tracks in any other region, they'd run exactly the same way, I've done that before, even.