I think negative emotions are severely diminished by Enlightenment and I think Emotional Mastery gets you closer to Enlightenment.
Would there be a need to master the positive emotions or just the negative ones? For me, it'd just be the negative ones as I'm perfectly content with positive emotions. So we're basically talking about rewiring ourselves to not have thought patterns that bring us to suffer.
To do that, we'd need to become aware of those patterns, find their root causes and use awareness and observation to change them.
Off the top, I'd venture to say that judgment and attachment/desire are the primary culprits of negative emotion, which are also what Enlightenment teachers preach to undo.
For me and my situation, the need for Emotional Mastery or the elimination of negative emotions that I impose on myself is currently more important than Enlightenment, and I think that's probably the case for most people. To become calm and centered and not so worried or agitated that you can't even practice spirituality. Strategically, this could potentially fast-track you to Enlightenment.
Emotional Mastery is a good target but I think that if you could reduce the negative emotions causing you the most suffering, you'd be happy just cutting those down by 50% and then Mastery might be a waste of time.
Either way, I agree that this is an important subject and definitely something to consider.