iTunes 12.4
purchaser
Along with downloader Apple ID/name (mentioned earlier), there are also purchaser Apple ID and purchaser name properties of track.
media kind
Previously, one could only change the video kind of a track. A new media kind property handles switching among alert tone/ audiobook/ book/ home video/ iTunes U/ movie/ music/ music video/ podcast/ ringtone/ TV show/ voice memo/ unknown. Changing this will place the track entry into the appropriate library; it will remain in any current playlists. Again, another highly desirable ability, AppleScript-wise.
cloud status of a track is a Thing
iTunes 12.4 now has a new cloud status property of a shared track whereby such a track will be one of the following: unknown/ purchased/ matched/ uploaded/ ineligible/ removed/ error/ duplicate/ subscription/ no longer available/ not uploaded. This has been long in coming.
description of a Playlist now 'Scriptable
You can do this:
tell application "iTunes"
-- the selected playlist
set thePlaylist to (get view of front window)
-- write the description
tell thePlaylist to set description to "This is my favorite playlist!"
end tell
This changes the description for the playlist in Playlist View:
iTunes 12.4 Released
Apple released iTunes 12.4 today. It features a significant UI change as well as updates under the hood. And AppleScript additions!
I've just installed it and note these AppleScript changes right off the bat:
current track - now recognizes tracks being played from "For You" and "New" sections. The tracks will be URL class.
download - originally for podcast episodes, now includes the ability to download cloud tracks or playlists to your library.
select - tell iTunes which objects you want to select (as opposed to selection objects already selected manually). [UPDATE: This is incorrect; see here.]
downloader Apple ID and downloader name properties of track.
New subscription playlist (an Apple Music playlist), miniplayer window and video window classes.
I haven't tested any of these very thoroughly yet. In fact, only current track. And of course, there is likely more stuff to discover. More as it develops.