P: RGB Parade and Vectorscope in Lightroom?

Thanks but that's really a workaround. shouldn't there at least be one plugin in the world that does this ?

No, it doesn't exist. This has not been something that people do in the stills world at all. My guess is that it will become more common but currently I don't think anybody has thought about this. Also note that you can't really write a plugin that easily embeds into the Lightroom interface so that route wouldn't really work. You can make a window popup but there is no way to have some dynamically updated window such as a scope you would use in color grading video so you could immediately see the results of your slider changes. So Adobe would have to supply something like this. Therefore what I would recommend is to submit this as a feature request on http://feedback.photoshop.com . Many features requested there get implemented over time.