One non-traditional way is to have the player write the call-to-action for their PC.
The traditional way in Classic Traveller is to have the players roll for a patron encounter (throw 5+ on one die, or 4+ if you have Carousing-1+, checking once per week). The players still have metagame knowledge, but it's a bit narrower than the examples I gave in the OP - in the fiction that patron quickly reveals that they are looking to hire a team of "specialists", and the players' knowledge that there won't be another patron encounter check for a week corresponds at least roughly to the character's knowledge that the number of patrons (ie people with ready cash to pay freelancers to do weird things) is finite.
I tend to share hawkeyefan's preference for some sort of immediacy over the slow drawing in.
The Heart RPG has a pretty great bit of advice for GMs: don't be coy.
I think there's a lot to be said about establishing a clear direction instead of trying to slowly tease out information in an attempt to woo the players into taking action. In Heart, the PCs are all "delvers"; they're all people who go exploring in the tear in reality that is called the Heart. So that's what the game's about. It's a clear premise and it is baked in, and you can just get to it rather than trying to entice players to engage.
But other than the initial premise, the game does something else and it offers "Beats" to each of the players. These are a list of achievements or goals for the players, and every session they'll pick two active ones to try and complete in order to gain an advance. So the players are constantly selecting their goals of play, and the GM is meant to incorporate those choices into the events of play whenever possible.
The GM is responding to the players' prompts rather than the players responding to his.
I think I previously mentioned this and you cited the similarity to the Marvel Heroic RPG; I've since heard Grant Howitt, one of the designers of Heart, confirm that's exactly where he got it from.
So there's some initial constraint at the start of play.... PCs will be delvers who explore the Heart... but then once you get going, the players are going to be choosing their own goals regularly during play. There doesn't need to be the "hook" of having the sage show up and drop his papers or anything like that.