I wonder if there could be tracks that are in more styles than only -desu/-masu and informal level. I mean, everyone learning Japanese is thaught that it's good (sometimes even extremely important) to know keigo, and I know there are some lessons on this site and elswhere where they focus on keigo. However, I think that many learners in the end "get stuck" in the -desu-masu-forms, because they are after all the most commonly used in textbooks as well as here. And I myself have experienced some embarrassment not knowing enough keigo when talking to superiors in Japan, or not understanding what the clerks in the shops are saying. Simply because I was never enough exposed to or in other ways "forced" to learn keigo.
So I think it would be very helpful to learn the various levels of politeness not only in theory but also in practice by hearing longer all-Japanese soundfiles in these seperate levels only. For example some audio blog episodes with only keigo, some episodes with only da-form, "de aru"-form, girls' language, boys' language, rough language, young people's language, elderly people's language etc. It would be a good way of getting used to the forms, and hearing them being actually used and not only talked about.
Also, for people being interested in old Japanese (like me ), I think it would be nice with some tracks (or videos with the text being shown) with for example bits of old literature (Japanese originals as well as translations) from various eras. Maybe with explanations (in English of Japanese), or just "translations" into modern Japanese attatched to them.
By the way, does anyone know any good site where one can study some "kanbun" (Chinese classics)?
Oh! And I personally like those tracks about Japanese dialects, and would love to hear more of those!