This one's a little hard to answer for me because I don't know where the 'design floor' is anymore for MMOs... lessee...
1. Most NPCs should have visible archetypes or classes that affect their dialogue and behaviour.
2. Some thought should be put into how those NPCs interact with others, the world, and PCs, based on those known Archetypes.
3. Some storylines/quests should have 'slots' that are filled by the nearest reasonable NPC with the correct Archetype/Class, i.e. there's a quest that starts with a Bard because it's that type of story, so no matter how the server develops, players know to find a Bard NPC in a City Node to see if that quest is available to them.
4. Different Archetypes could have slightly different ways of interacting with certain objects or micro-PoI, nothing too fancy (not like Neverwinter where you just carry around Class-specific tools to poke differently named treasure boxes), nothing too absolutely required
5. Different Archetype NPCs can expand on this also by offering different small services that you associate with them.
6. I'd also suggest some Archetype-Augments being locked behind questlines, but I'd bet the more devoted audience of the game in the longer term will just find this annoying so maybe not.
7. Some stories could also have 'slots' like this, particularly story Arcs that have a 'race' to be the first party to clear something. Assuming that the party managed to have all 8 Archetypes, as intended, when they clear it, the story/historical record could be written with a story-role for each Archetype, and then the player of that Archetype gets their name inserted into the historical story record thing. Obv be careful with this, since it pushes on people's RP, but I bet y'all have writers who have this skill.
I'd say the most important thing is to make it as clear as possible, which is somewhat harder for Ashes because it can't necessarily count on people being able to recognize an NPCs Archetype by their gear in any way.
Obviously there's the other standard approach of getting Allied NPCs involved in combat so they can show off their moves and help with the storytelling in that regard, which serves the alternate purpose of sometimes giving players the option to fill a
specific
storyline slot in an NPC group as a sorta-solo activity. In contrast to most other 'You are the main character' games, it could be a bit better tuned so that the thing you're required to do is relative to your Archetype. Work those in-engine cutscenes, etc.
Games (I hope) are filled with historical or specialized stories with Archetype/Class/Job relations that involve this, the above is all just 'extend this a little more' which is something a lot (I hope) of games do but some don't anymore.
What I don't want, despite my love of 'important NPC who pulls you in to do some things they don't have time for', is the Neverwinter style of it where the only way you know about an NPCs Archetype/Role is when they introduce themselves and then maybe you read up in their history somewhere.
Nearly every NPC that I consider properly memorable across all the MMOs I play, I've seen them fight, or I know how they fight, or I at least know how/why they don't fight. It doesn't have to be 'fight', it can ofc just be 'live', as long as they actually show it, which, in the case of this question, should be through their Archetype.
Hope that all even remotely touched on what the team is actually trying to ask.