Well, what Rigwyn suggests could perhaps be done if it can be 1 generic text to be used by all NPCs instead of the current big red text (an NPC would then just have a text bubble saying "NPC has no quests at this time" or something similar).
While Ligh's suggestion is certainly nice, it would require a whole host of different messages (which we do not have), and in addition, the potential for getting spammy is certainly there. So that one would probably not be viable to implement right now.