A detective approach sounds interesting.
Here's the kicker: The "new narrative or idea" on this thread is less about joining NCPD "in general" as that's now likely out of the picture. What but compromise or alternative would be viable?
NCPD ties or "joining" particular units
You can avoid the "faction dilemma" from a dev or plot perspective and still offer leeway, like you could often not formally join big factions in Fallout New Vegas (like Legion, NCR), but you could
a) closely work with them to be considered a quasi member, even run around with their gear in a certain way
b) join smaller not as important factions and groups, like the BOS (in that game its role isn't as big I like to think), the White Glove Society, the Kings, etc - groups where joining or not has no big impact on the main plot, but you can still "belong" to some group officially or more or less in practice
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To mirror this, I imagine what could be fun and a working approach is just that: "joinable" (or "working with") "mini-factions" or particular units.
For NCPD, I imagine it like this, as I stated in earlier posts in different forms:
You can basically join or closely work with MAX-TAC or some sort of investigator unit or detective squad or branch and get perks out of it - ideally some sort of uniform or gear you can use, maybe next to other perks like abilities or changed speech in some situations or "quests"
Why did I pick MAX-TAC and then some more detective focused branch? Because those would be less intrusive than becoming a "rank and file beat cop" or officer that would potentially meddle with the main plot or the premise of "no joinable factions and an independent V".
MAX-TAC? Why? I'll just refer to this quote:
"They walk like us, talk like us. MAX-TAC are just criminals with a badge„
— Anonymous Punk, Protect & Serve
V's personality we can see in the shown footage so far would not need to be "warped", the (cyber)"punky" style can be retained, and MAX-TAC itself can be a logical source of what would often be higher risk missions in hunting down psychos, and neutralizing them, or perhaps responding to active situations in a support role. You even formally joining wouldn't necessarily impede the plot unless the main plot somehow has parts that cover this unit in a bigger detail or as antagonist in some mission.
It would just fit and you could do missions for them.
Detective stuff? I bet most people like it and since it's more so a special thing, "joining" or quasi-joining through close ties and supporting them would also be interesting and give you more Thriller-like content and more, next to pure action.
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Long story short, with slight tweaks and compromises you can expand the possibilities of the player, add more side content and if you just "tweak it right", you can make it seem like you basically do police related work, whether that may be as someone with "close ties to NCPD" if the players actively want it, or as quasi-member of particular units or branches that perhaps operate a bit outside of the usual MO or regulations.
It would be the best compromise I can imagine, for all involved.
But alas, we'll have to wait and see. I am very certain by now, the devs are aware of a particular interest in the area and either did consider it or are perhaps still considering it, or may do so a bit later. On the rest, I can only speculate, but it would be nice to be able to somehow work with NCPD beyond simply, say, go to a terminal to select random "bounties" to then hunt.
Not asking for a fully fledged NCPD career. Well, that would be nice, but it's not in the current or given scope. But a bit of leeway here and there for the Judge Dredd and Co. fanboys would be nice.
Before I repeat myself and make this post longer, I rest my case for now, eagerly awaiting more replies and discussion