I use Widgetlocker for the lockscreen so I can customize it however I want. You can find all sorts of icon packs, uzips, custom sliders, fonts, wallpapers ect. for free all over the Web if you search.
As far as customizing the lockscreen, I don't really see any limitation with it. Granted if you have a pass code enabled you still have to input it to access shortcuts but that's what the security is supposed to do.
Other than that you can design any screen you desire and don't have to be rooted.