I understood what you said, I don't understand why you think that.
You claim it's a MAJOR reaon Nintendo delayed the eShop, it isn't. If it is, Nintendo would basically be waiting to give hackers full use of the system, instead of bricking them with the first unannounced update. If in the first update there is new security, hackers simply have to wait for it, then hack away. After that, they no longer need the updates. Why would anyone hack the system BEFORE such a major update only two months away? You don't think hackers don't read the internets?
Also, even if DS backwards compatibility was powered by the 3DS's architecture, I would assume that putting in a DS game would put the system in DS mode that would shut off some power 'sipping' features of the 3DS like; 3D, StreetPass, AR (non-DSi games), etc. In the DS, because there were two slots, you could choose what to load.