This is just a quick thought that I haven’t thought much about (it’s tea-time) but:
We can import our own materials into lingQ, and use them as our own study materials, right? How do we assess the level of complexity of the material, other than using the “Blimey that looks hard!” rule-of thumb?
I wondered about using standard readability tests like the Automated Readability Index (see, e.g. Tests Document Readability). i’m not yet clear what all the stats actually mean, but I copied in some Cyrillic and at least the program didn’t fall over.
Clearly you can’t compare readability across languages. Russian is always going to score worse than English, because the inflexibility of the grammar and the prefixes and suffixes make for long words and long sentences. But it should work to at least rank your materials in a given subject, and help you decide whether to study Tolstoy before or after Tolkien.