@VonMagnum: you're wrong regarding the slideshow - it simply takes a list of all photos, randomizes it, then plays that randomized list in order. If you're not seeing a particular photo, perhaps that photo couldn't be loaded for some reason?
No idea what you're talking about with ProjectM - if you haven't already done so, please post a bug report (or bump the one you've posted).
As for your other issues, yes you need to edit advancedsettings.xml for grey black bars. This is because 99.99% of users don't care about it (yours is the first comment I've seen in a few years).
You could try upnp for multi-xbmc box stuff. It's not ideal, I agree, but really we as devs need a push here to improve it - more people jumping up and down about what works well and what doesn't work well (or not at all) would help I think.
XBMC supports some form of airplay - no idea on what as I don't have iOS devices.
XBMC also supports lyrics in ID3 tagged files at least. The lyrics addon should be obtaining them from XBMC. Perhaps the file types you use haven't been hooked up - place a feature request with an attached file + whatever info you think is needed and someone will no doubt get on to it.
Lastly, you can remap just about anything keymap related. Your universal on an ATV might have some issues with this, and I agree that it's not easy to do so.
Improvements (and even just ideas for them) are always welcome
Cheers,
Jonathan