Ok something very interseting to report! Mario 64 DS I got to boot BUT only if I had a Mario 64 DS cartridge inserted! So it appears DSiWare running in DS mode has slot-1 access. It appears to be reading the save from the cartridge. It won't boot if I have anything else inserted into the slot. So it's not simply "launching" slot-1. (I made sure the TID field wasn't configured to do that).
So it actually reads the save from the cartridge. Now maybe! This can still be usuable for something. Like altering access control settings of a DSi enhanced cartridge. (like the iEvo for example!)
The console reads the game from NAND, but all cart reads/saves willl come from the iEvo being inserted. Someone should dump the rom used by iEvo and try this.