the reason other carts cant function as both, as there's no room for both. the AK2i has a larger NAND on it allowing for both, new cards built for this have a switch that itther switches "Pages" or nand banks from one ment for ntrboot or one for cart functionality. i dont think one's come out yet to copy the AK2i in this manner (sofar the closest really is the R4i Gold + )
im not sure how other card FW's Worked but if you pour thru a proper dump of the AK2i, you'll find an actual full DS Rom dump within it. (big reason you cant directly upload or link FW Backups of the AK2i just the FW updaters