Ok, here's the thing, the 3DS theoretically it can run any DS rom with a flashcard, this is possible since the 3DS is backwards compatible with the DS, therefore, making the use of flashcards possible for the loading of any NDS game that you want, the thing is, if you look the 3DS in a hardware perspective, the CPU of the 3DS is able to do it since said console is able to just switch off the system, and "downgrade" all of the procedures in order to fit the DS, if we want to do it with an SD Card, we would need a kernel exploit able to control EVERYTHING the 3DS has, including the possibility to give orders of any kind.
The 3DS Homebrew Launcher will not launch any kind of DS games (Or at least those with 9.3 and superior) but even then it isn't possible, not because we don't have the kernel exploit, if not, because this one doesn't have full accessibility to the most internal commands of the 3DS, we may have control of the 3DS games with cias, and with that we can play any kind of 3DS game, but NDS games are another thing, remember that the 3ds processor has to be downgraded in order to play them, and we don't have a kernel exploit powerful enough in order to do that.