Extending the skill tree
i always want duolingo to extend the tree into a higher level, say b1-b2 and c1 to c2. how about if we can use our useless lingots to buy the new branches of the tree?
There is a material difference in how you teach a beginner and how yo teach an intermediate (or an advanced student). While a beginner app can pass with just sentences and words, a higher level one will need a lot longer texts and a lot more variety. The A levels are the textbook language, in B you start moving towards your own phrases and C is... not textbook at all.
Checking what is correct and what is not becomes a HUGE problem the more you add. Now you know one word (or two) for a specific thing; the B and C levels add synonyms and special meanings and what's not. We already have issues with the course not recognizing all valid options; the problem will be much much much worse in the higher levels. Unless you switch to just asking for set phrases and "select the correct choice" exercises... which makes it useless for an intermediate student.
Look at the German tree. It technically gets you to a very low B1 but it has gaps. If it needs to get to a real B1, you need at least as many skills as we have now and we need a few other types of exercises (or the stories in the lab need to be extended a lot more). Let's call in 250 skills altogether for B1 (I'd argue you need more but let's be nice). Double the whole thing for B2 again (now we are ~500 skills). I am not even going to start on the math for the C levels. And the lessons get longer the lower you are in the tree so... by skill #500, a lesson will be 25 minutes or thereabouts? Alternatively you split them into smaller ones and your numbers explode.
Don't get me wrong - I'd love the options but it needs a totally different platform. Why would they do that for German instead of developing 10 new languages at the same time?