As an iOS Developer I would not recommend using RubyMotion to "learn" just hunker down and learn Objective C it's really not that difficult to pick up. Currently I would also give the the same advice for Swift - You're better off learning Objective C and then learning Swift since there is still a lot of interaction between the two (this may change in the future).
"I’m still convinced I wouldn’t have gotten this far without RubyMotion, and as a learning tool its value is immeasurable."
I contest that this is not great advice for other people interested in learning to program for iOS, maybe for Nick it's applicable (I believe him) but in general, just learn Objective C followed by Swift.
I haven't really looked in depth into merging separate iPhone and iPad apps, but I think they made a mistake by optimizing short term. When I get a new app, I definitely don't want to download two different apps: one for each device.
I think they'll be missing out when people download for a single device and miss out on the app on their second device.
Basecamp for iOS is one of the shining examples of how well a hybrid mobile/html5 strategy can work. Every fellow developer has been genuinely surprised when I've told them that Basecamp Mobile is a hybrid app, even staunch native proponents. That's the gold standard of a good hybrid app.