Could Trader NPCs be modified to not care what they receive? As in they'd accept any pokemon? (unrelated- do they currently spawn in the wild like move tutors?) This functionality may be redundant with Pokegifts but could they also be modified to just GIVE you a pokemon? Obviously once per trainer or even just once ever before disappearing.
Could trainers be customized to BECOME chatting NPCs after they've served their original purpose (Trader, Trainer, etc.) instead of just disappearing or being told you can't interact with them anymore. Even better if you could also add chatting npc dialogue BEFORE they serve their intended NPC purpose. This would allow the trainers in gyms to give hints more than once after defeat or give more meaningful dialogue to gym leaders before and after battling them.
What about NPCs who give you an item the first time you speak with them (or once per day or only the first trainer they see, etc)- then have alternate dialogue thereafter.
Could chatting NPCs offer different dialogue if you are holding certain items (or Pokemon). It would be a great tool for adventure map makers but in the main mod it could allow gym guides to congratulate you once you've got the badge for their respective gym in your inventory.