Well a magic infused instrument wouldnt be a stronghold type quest would it
Different object ... same problem.
My Rogue is lightarmor wearing honorable blade dancer warrior ...
> Rogue quest is themed for either thieves, or assassins.
My Bard is actualy infiltrator assassin ...
> Bard quest is themed for entertainers.
My Barbarian is actualy a king, who likes to get shits done himself, rather than use his army (you might heared of him, his name is Conan)
> Barbarian quest is themed for bulky idiot who just want to smash as many heads as possible.
My Warlock gets his power by accident and his lifetime quest is go get cured of this shit.
> Warlock quest is themed for people who desire more power, no matter how coruptable it is.
See the pattern yet?
Secondly if for example you are a "evil" paladin and go do the paladin strong hold quest whats to stop you killing the paladins instead? Whats to stop larian from giving you a quest line to corrupt the paladins.
I dont really understand the first question ...
You go to paladin strongold take a quest ... and then kill everybody bcs ... "? evil ?" *cofused smilie*
Whats stoping Larian, thats a lot easier question tho ... money.

You see there are 12 classes if i remember corectly ... now, every single one of them have several sub-classes that makes them a lot different often, but lets ignore that for the sake of sanity ... any one of them would need to be Good or Evil ...
That alone would mean that you need to create 24 Quest chains, of wich 23 would be possibly completely wasted, bcs your character can allways be only one thing, and there is no ensurance that people would repeat the game.
Isnt is a lot better from developer perspective to simply make 24 regular quest chains, that anyone can participate ... wich will contain some class specific chocies, and decisions here and there?
Yes it is.
You demand to run your keep?
Why not ... everyone get a keep!
Paladin can afterwards decorate it with his holy symbols, and have acolytes there ...
Druid can afterwards cry in basement in desperation that there is no way to make this in tune with his class ... or make small garden in the yard ...
Barbarian can decorate it with skulls and organs of his fallen enemies ...
Wizard can display various tomes, scrolls, maps, artefacts, and objects of study ...
Etc.
And finally it wouldnt be a non class person refusing work as you said
In bg2 if u wernt a warrior you wernt given an opportunity to run the keep
If you were not a druid you couldnt take over the grove
If you were not a thief you where not given the chance to run the thieves guild
Exactly the point man ...
You see, i didnt say that "non class refusing the work" ... i said "non class not being even offered the job" ...
Only Fighter can run a keep?
Why? What is so special about fighters so they are the only one fit to run a keep?
NOTHING. Thats what.
Its just obsolete gamy mechanic forcing you to adopt stereotypes game developers picked for you.