In every single Pokémon game, a battling NPC will always talk to you before starting the battle. In Pixelmon, there only is 1 line of text, which is fine but quite underwhelming if you want to make something unique.
If it was possible to allow dialogue for every kind of NPC, with the battler as example, if their UUID is specified in the json file belonging to the custom quest, it would allow characters in a long quest to have a lot more life and oppertunities.
I conclude with the suggestion in the 1 sentence that didn't fit in the post title:
Allow any kind of NPC to have dialogue like a Chatting NPC or Quest Giver in custom quests, if their UUID is specified in "NPC_TALK" objective in the json file belonging to the quest.