Is there a thread discussing splitting Diplomacy and Trading into separate skills?
Those 2 are not the same, not even close enough to be in the same bucket.
Diplomacy could have a moderately positive effect on Management. Diplomacy skill could also have a positive influence on trading and so could a (non modified) management skill. (0=no influence) with formulae expressing how much trading is enhanced by either.
They wouldn't be split just because the vague concepts can be interpreted differently. The skills are designed as needed for gameplay, and there isn't any point in splitting them again without the need for two separate skills. Technically it could be named to either Diplomacy or Trading, and that would serve the same purpose, but no feature plans require a second skill that can't be covered by this one.