Although Visual Editor is a huge step in user experience for Wikipedia, it only benefits authors, or at least conceptually so. Most readers who only need introductory information have little to no incentive to engage in editing. But these are people Wikipedia should rely on in finding minor bugs, spelling errors, missing citations, etc., in general proofreading. But current barrier on proofreading is still too high for general public to participate.
The current minimum steps for a Wikipedia reader with no editing experience to add a "citation needed" template to a sentence are the following:
1. Know the template system
If registered:
2. Open Visual Editor
else:
2. Search for template:citation needed
3. Insert the template
The first step is the biggest barrier under the assumption.
My ideal proofreading mechanism is proofreading as reading. I want to select any part of the content and choose from a list of proofreading templates right away. Such UX can also serve to teach readers that Wikipedia is not an authoritative source, and to cultivate their habit of critical reading.