"Fast loading time" was never something mentioned or talked about that I saw. More that a gig of ram was (for now) reserved for OS usage. That doesn't necessarily mean reserved to create super fast loading - it could be for complex applications, loading multiple applications at once, running complex services in the background (like Miiverse).
As for what Nintendo has been doing - personally, I'd figure they've been working on the fundamentals of the technology by launch. With all that's come to light about the nuance and complexity of making the gamepad work right, it seems a great deal of resources when there. On the OS front, whether we like it or not, all of this stuff involves Nintendo spreading out into unfamiliar territory. Network technology, multitasking operating systems, etc, is a new business. It seems pretty clear that they were and are working on the OS full tilt, constantly.
One point of interest: for all that people point to the Xbox OS / Xbox Live as the "gold standard" for modern game consoles, it doesn't often seem taken into account that it was designed by a company that specialized in operation systems, networking, and internet. That's a powerful advantage to have on your side, such a pool of experience to draw from. If anything, Microsoft has a nearly unfair advantage over everyone else (not just Nintendo) in this area.
