iTunes 12.4.2 Released
Apple released iTunes 12.4.2 today (along with updates to all current OS) which addresses a play back issue with short songs in Up Next. More if it develops.
About Sierra Public Beta
Apple's Sierra Public Beta program allows registered participants to download and install the latest developer builds of macOS 10.12 before its ultimate final release in the Fall. If the public beta program works like it has in previous years, developers will receive updates first and then a week or so later the public beta testers will get a version.
As a registered Apple developer, I've had access to macOS 10.12 since WWDC in June. As far as I've been able to tell, any scripts or apps from this site that are already downloaded on a machine that is updated to macOS 10.12 should work fine. But Apple has introduced new security features in macOS 10.12 that may affect some scripts or apps if they are newly downloaded to a Sierra beta machine (they won't behave badly, they just won't be able to be launched). Therefore: unless a script or app is specifically described as supporting macOS 10.12, don't assume it will work on Sierra. To be clear, there aren't that many downloads that will be affected and I'm updating those as promptly as I can.
Issue With Copying a Newly Converted File
I've been going crazy trying to track down a problem using AppleScript to convert a file and then duplicate the newly converted file's track entry to a playlist. No matter what I tried, the original pre-converted track is copied to the playlist and not the new converted file. Here's a stripped-down example:
tell application "iTunes"
set oldTrack to item 1 of selection
-- convert oldTrack and get a ref to the newTrack
set newTrack to item 1 of (convert oldTrack)
duplicate newTrack to somePlaylist
-- ...but oldTrack gets copied
end tell
Come to find out, iTunes 12.4.1 gets fussy about converted files when iCloud Music Library is active. As soon as the new converted file is created (again, via AppleScript) and added to the library, iTunes goes into its "Waiting..." mode—waiting to upload the file to the cloud. This apparently prevents AppleScript from doing anything with the new track entry.
This reminded me of how iTunes will warn you about editing a track (that is, about using Get Info) while it is waiting to be uploaded:

Strangely, all the properties for the new track are available. So, I tried adding it to the playlist using its location (file path); I tried persistent ID'ing it from library playlist 1 to get a reference to it; neither worked.
It wasn't until I shut iCloud Music Library off in iTunes > Preferences... > General that a newly converted track entry could be copied to a playlist. After some more experimentation with iCloud Music Library turned back on, I tried setting up a loop that waited for the cloud status of the new track to change to uploaded. But, since it can take several minutes for this process to be initiated, I abandoned this.
Primarily this will be a problem for Quick Convert, which has an option to copy converted tracks to a new/selected playlist (and, I suppose, any other script that works similarly):

If iCloud Music Library is ON, the "Copy new tracks to playlist:" option is ineffective.
The player position Bug Fixed
This bug that prevented setting the player position while the player state is paused is fixed in iTunes 12.4.1
iTunes 12.4.1 Released
Apple has released iTunes 12.4.1 which fixes the Crossfade bug, problems with Voice Over and Up Next, and restores the Reset Plays and Convert ID3 Tags features.
NEW: Reset Plays
Even though I had posted a script workaround to emulate the now-removed "Reset Plays" feature, several users had suggested adding a few additional settings. Plus, some people were just not sure how to get that script onto their machines.
Reset Plays is a downloadable variation of that original script that, in addition to resetting Plays and Played Date, also resets Skips, Skipped Date, Rememebr Playback Position and the played property.
Can't Replace "Convert ID3 Tags"
Apple has removed the "Convert ID3 Tags" command in iTunes 12.4. I don't know why. I didn't use it much myself but many users needed to convert the metadata ID3 Tag version so MP3 files imported or converted with iTunes would be compatible with other players.
There is no AppleScript command or property for iTunes that is related to this so no purely-AppleScript workaround is possible. Interestingly, SoundJam's AppleScript dictionary had a property to read—and possibly write, don't recall now—the default ID3 Tag version. It didn't make the trip to iTunes.
[UPDATE: the Convert ID3 Tags feature has been restored in iTunes 12.4.1.]
UPDATED: Smarts v1.3.2
Smarts will save and store the criteria of an iTunes Smart Playlist—the smarts of a Smart Playlist—as a template so you can reload it into iTunes later.

This latest version makes accommodations for changes in iTunes 12.4.
Smarts is a free download from The Mac App Store.

On the latest episode of