[lbatx]

You make an interesting (unsupported) assertion here. You, who find talking to an IRQ controller, real-time clock, etc. interesting, find Scheme boring, therefore others (who may not share your interests in such details) will also find it boring. Bit of a logical fallacy there...

[acbart]

I've run a lot of surveys of introductory students trying to find what topics are more or less interesting to them. A part of my dissertation was committed to it, actually.

At this point, I'm more or less certain you'll rarely find situations where you have a mass-appealing context. One students' dream context is another students Most Boring Possible. You're probably better off having many diverse contexts and hit all the MUSIC guidelines (eMpower students, Useful to their long/short term goals, make students Successful, make it situationally and domain-based Interesting, and give people opportunities to demonstrate that they Care about each other).