SuperCard could probably do it if they were interested.
For someone else to do it, they'd first have to reverse engineer how DSTWO firmware and firmware updates work in order to create their own firmware for it. Not an easy task.
The way DSi mode works, it's not as simple as just replacing the DS header with a DSi header, I believe the iEvo actually exploited a game in order to run unsigned code (as DSi mode won't normally allow it), and had to include part of that game on the cart. And who knows if the DSTWO EOS would even work in DSi mode, since it's not designed for it.
Even if it worked, only a limited number of DS games are DSi enhanced. If you force non-DSi enhanced games to run in DSi mode, wifi won't work at all. And DSi mode generally breaks homebrew that isn't DSi-aware. Because of this, it's of limited usefulness.