Not cost much? You realise that sometimes just changing a small UI component can be a major issue, right?
Adding an entire new module isn't a small exercise, and even if it doesn't cost much in cash it costs in terms of development time and resources working toward other things.
That's all fine, if there are actually enough users who are willing to pay for those features. As it stands, the attitude seems to be "oh, this should be easy, let's just incorporate design features from ID and Acrobat Pro and mesh them into LR and, yeah, don't charge me any more for it."
That's *not* going to excite Adobe to rush to add this feature :-)