[pkscout]

Was I missing anything else juicy that it supplies and I should add support for?

Everything is documented in the wiki. The only thing I don't see in your list is similar artists, and I'm not really sure how valuable that is. That information comes from Last.FM, and at the rate they are closing access to their information, it's hard to say how long it will be there anyway.

1. Would it be possible to have a setting in Artist Slideshow to enable/disable the logging (only when XBMC logging is on) as now I have it installed, if I enable debugging on one of the other addons to see what is happening - I automatically get Artist Slideshow logging as well (can make the log file a little harder to read).
   
2. As I have launched it from another addon - I was wondering if there is an interface on Artist Slideshow that I can call to "pre-cache" an artist's information (It would help reduce the delay in data loading for the Sonos addon) - especially when the Sonos Addon can see what is coming up next in the playlist.
   

I might look at #1, but it's an exceptionally niche request. I also think it would complicate things for people submitting debug logs for troubleshooting.

#2 really isn't a viable option. AS is designed at it's core to act on the current song and wait for a change to do something new. It would require some pretty substantial changes to do anything else. The majority of the delays come the very first time you listen to an artist. After that it's pretty quick to show existing artwork.