I know the autoplaylist has an auto-sort but isn't not possible for my custom playlists, is it? If not, I'd like to request it as a option.

When do you want foobar to auto-sort exactly?

I'm guessing when files are added.

Gee thanks.
From where?

The library (and if so which from which library plugin) or from file->Add... or Every time a playlist is made active?

These would all have different solutions.

For example, I have a "party" playlist. Whenever I drag and drop a song into it, I want it to automatically sort.

When I use the library with the autoplaylist plugin, it already auto-sorts but I want the same to happen for my "party" playlist which doesn't use the library.

On a related note, it would also be nice if the autoplaylist plugin produced a "New files since last scan" playlist. It'd be nice if I can just dump all my new songs into my music folder, do an autoplaylist scan, and get a "New files since last scan" playlist so that I can tag and replaygain the new songs. Currently, I have to save my songs to a temp folder, create a temp playlist, add the new songs to the temp playlist, tag + replaygain, remove the temp playlist, move the songs from the temp folder to my music folder, and finally do an autoplaylist scan.