Golden merchandise: Doulingo staff, listen!
Reading this post (https://www.duolingo.com/comment/11666832), an idea struck me: Why after finishing the tree, getting it golden, (and if you want to be pushy, only after reaching level 25), Duolingo could offer to those finishing some unique and exclusive golden merchandise, for a price $$?
Think about this, Duo owl in different sizes (depending how much are you willing to pay for it) engraved with the name of the student, language learned, and even how long it took to get it (or from what date to date). it's not going to be cheap, as the level of unique detailing involved -but I guess they can produce golden owls in masse and stick later a plate with the data.
Also, there is another kind of exclusive merchandise that can be offered: Shirts with a similar design, but only sold to those finishing the tree golden and level 25.
I guess that can be seen as an ego booster kind of thing, but hey, live a little lol
That is a way to get some money for Duo's coffers. it's kinda like: you don't pay for the course if you don't finish it.
Just an idea.
One of the problems Duolingo is working on at the moment is that there are a lot of people who finish the course really quickly, without having kept it gold, and without having learned much. They're trying to slow learners down, and discourage us from rushing for the end of the course.
Maybe the exclusive merchandise could be available to those who'd finished the course and kept it gold for a while.
The motivation here is you will only have access to the golden merchandise if you end the course. And you will get the cup/owl/t-shirt personalized for you.
And if you want to buy a t-shirt from Duolingo, they already have that, here: http://gear.duolingo.com/
The idea was to offer something unique to those conquering the tree.