Well, I'm libertarian enough that I think all thread prefix choices have gotta be strictly voluntary, at the discretion of the thread-starter, but I've no problem with your suggestion in that sense, bw. Admittedly, it doesn't make too much sense to not use "Lyr Add" when you want do add lyrics to the DT, though. A lot of this is just plain common sense. I use BS for just that purpose when I start a non-musical (and sometimes a non-folk-or-blues) thread. Maybe for the "my thread is serious, it's not BS, but it's not music either" threads, maybe NM for Non-Musical threads could work.

Chris