I get what you mean and, for the most part, I agree -- I'm not really sure I'll actually use this, but I thought I'd give due diligence into the research.
I'm writing this framework for the college where I work -- it's essentially a collection of classes that perform various functions. For instance, a Student class for routines relating to students, and LDAP class for methods that relate to pulling information from Active directory, etc.
Currently, every time I serve a page, the whole of the framework gets included and loaded, hence the dependency injection. Just from a performance/resource standpoint it makes sense. Trapping the error and trying to include the file, instantiate the object and rerun the code that caused the error is, I guess more to keep the "flow" going when your writing in a zone... to know you can just call a method in one of the established classes and not worry about having to go up to the top of the page and instantiate it.
But yeah, the more I think about it, the more I think it's probably not a wholly great idea.
Maybe if I have a class wrapper like $Framework->$Student->method() and $Framework can trap for the child object and instantiate it before going on to that method.
In any case, I appreciate the feedback and thoughts.