A thought about prestige classes

[Spooky]

Ok i was making some builds last night and i came up with a build i liked but had 2 prestige classes.So i thought that 2 prestige classes could be possible,but not easily achieved.

My thought was that when someone was ready for a 2nd prestige class he would consult a DM and that DM would give him a quest,very "close" to his 2nd prestige class.For example:
i am a lvl 10 rogue/10 assasin and wanna take 1 lvl of shadowdancer coz i miss hide in plain sight.I am letting a DM know,and the quest he gives me is:(since only SL takes Assasin) You must sneak into ancient one's territory and get this item (which only drops there).That is very close to "shadowdancer" as they practically live in the shadows so sneaking out should be something they can do.Also if u wanna be a WM in [censored] for example a quest could be clear an area alone by carrying only a [censored] sword (not shield) to prove its an extension of ur limb.

These are just the first thoughts however it would add a lot in this module and maybe give us all the chance to feel a build complete:D