as others have said, you need a critical mass on any one freq for the data to really be of use.
so, why not on a world wide basis use one dedicated freq for say 24hrs. if you cannot tx on a band, then just rx. this still gives good info.
if everyone gave it a week, it would cover almost every hf band.
so if its monday, it must be 30m.
david/wd4kpd