It would be great to see what it would look like with "Challenge For Change" as the main message and "EWB" as the secondary. I really like the "Engineers Without Borders" on the bottom of the design.
It would be great if we could incorporate the theme of 'choose-your-own-adventure' into the logo. There is an updated brief that describes a bit more about Challenge for Change now, if you want some more info.
I'm not sure about the light bulb surrounded by cogs - the EWB logo is simply the light bulb, so if that is used, it might be best to keep it as it is in the official logo, as the cogs are not specific to the event either. I like the shape of the runners but wouldn't mind seeing some other types of silhouettes for comparison. Or what about having runners holding small light bulbs like a torch? Not sure how that would look though.