For years, plenty of apps and services have used bookmarklets to pass the current webpage around for one purpose or another—blogging, reading later, archiving, bookmarking. Creating a bookmarklet on iOS is a frustratingly prohibitive process, but we might not need bookmarklets at all. If Apple added Document Sharing—which you may remember from some options as the "Open In..." menu—to Safari and enabled it to support simple web URLs, it could strike two birds with one stone. The first victim, or I guess technically victims, would be bookmarklet complains. Apple doesn't have to spend time and resources on developing a new technology, UI, and support—it could enable Mobile Safari with a feature iOS users have known for two years, and URLs could be passed to the many apps that were born to digest them.
Second, Document Sharing could go at least some of the way to satiate requests for Mobile Safari to support extensions, the bookmarklet's big brother. Of course, some extensions are designed to do things within the browser—add affiliate links to a blog post, dig up tertiary information about keywords, create a task—but again, the ability to easily send a page to another app could help with at least some of this.
Finally, Document Sharing in Mobile Safari would further promote an app-centric workflow on iOS. Bookmarklets are often designed to open another web service in a new browser tab, and let's face it, working on the web is a crummy experience. But even if they're wired to open an app, bookmarklets are still a colossal pain to install which cuts off most attempts at the knees. This largely confines Mobile Safari and its content to an island, making iOS's URL-to-app workflow needlessly tedious for anyone brave enough to try it.
If Apple added an existing iOS feature to let Mobile Safari easily pass a URL to other apps for bookmarking, blogging, and reading later, users would have a much better experience getting things done on iOS. They would probably bug their favorite services even more to get into the App Store, further padding that big ol' number Apple loves to toss around.
Everybody wins, but especially iOS users, who deserve a much better inter-app experience.