What sort of thread would be interesting?

The legendary Song Challenges certainly were to me, both amusing and enlightening. I would like to participate in a tune writing Challenge for given lyrics. The starter must be someone of sufficient authority to attract many competent participants. Other ideas along that line are welcome.

Controversial discussions can be enjoyable as well, depending on the number of constructive contributors. Banal and bickering messages must simply be ignored. Threads started by serious posters about genuine problems will rarely be hijacked successfully. In fact very few threads altogether are hijacked successfully.