This would be incredibly advantageous for web developers because it would allow them to charge for their web apps on mobile platforms and lock down the source code if they were distributed via the App Store. It would also make porting between devices a lot easier, although this wouldn’t be as advantageous for Apple.
Unfortunately there really isn’t much in it for Apple because it either involves a huge port of their libraries of a huge loss of design I’m apps. The bare minimum is to allow current (major?) apps that rely on UIWebView for the majority of their content to access Nitro, ensuring faster performance.
Ultimately I don’t think that Apple will make HTML5 apps first class citizens on the App Store any time soon, but accessing Nitro could provide a major boost to mobile web apps.