New Lingot Uses
I've noticed as I have been using Duolingo, that Lingots don't have much value in the Russian course. You can purchase streak freezes and double or nothing, but that's just to get more Lingots. The timed practices are ok, but they don't change the learning process very much, they just allow you to get more experience points. I have a friend who is taking the German course, and I've seen that you can buy extra lessons with Lingots. The one my friend showed me was a lesson on how to flirt in German. It would be nice if the Russian course had something like that as well. Flirting wouldn't be a bad idea, and maybe a course on jokes or puns in Russian.
German has just two so called "Bonus Skills": "Idioms and Proverbs" and "Flirting". They cost 30 lingots each and are available very early in the course (after just 4 regular skills), when they look like puzzles (especially "Idioms and Proverbs") and therefore don't give you much. It would make sense to buy them when you are close to the end of the tree.
As an extra material they are Ok, but in my opinion they are not very useful to put it mildly. Similar Italian skills are much funnier. I guess it all depends on the developers' choice and creativity. So yes, they can be entertaining, but if you want to find some use for your pile of lingots, these two skills wouldn't help you much.