Yeah, that's unfortunately the big hangup that keeps me from adopting Apple (mobile) stuff past app development reasons. It's too limited really for hacking and modding. Sure, there's some groups out there that mod with jailbreaking to add features, but if you want to add an entire OS, you're just kind of out of luck. There's a small part of me that likes seeing how I can get around all that without source, but after a while, I rather stop fighting it and just use a platform for modding/hacking that makes it easier. Even custom ROMs for Android are usually a bit quirky and full of bugs if they're running on anything other than Nexus devices, due to a mismatch in driver versions and the OS version much of the time.

If you want something to just hack around on and mod stuff, I recommend getting a Nexus 7 for that and use your ipad for your normal usage. They're cheap, battery life is good (as far as Android goes, it's 7-8 hours for me normally). Ubuntu for tablets is to be supported for it and there's an unofficial webos port for it out as well. That plus the entire AOSP android source and plenty of ROMs out there to take features from.

Unlocking + rooting Nexus devices is dead simple. Basically plug into USB, run a few terminal commands and you're done. Granted it makes taking updates a bit harder (if you mod past this), but if you're rooted and unlocked, you usually do it yourself anyways versus taking a direct update.