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 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.<p>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.