A couple of Correspondents have reported that fresh installations of Sierra do not have a "iTunes" folder in the User Library folder (~/Library/iTunes/). Traditionally, this folder contains the "iTunes Plug-Ins" folder and the "Scripts" folder (see my Download FAQ page for more details). Additionally, some third-party apps may use this folder for caching their own iTunes-related files. However, the "Scripts" folder is not created automatically and needs to be created by the user; and I believe Apple has lately inhibited the use of third-party visualizers such that the "iTunes Plug-Ins" folder may no longer be necessary. Perhaps, therefore, the ~/Library/iTunes/ folder is not created automatically anymore either.
To repeat: this seems to affect clean installs of the latest Sierra and iTunes 12.6 and later. If you already have these folders configured on your machine they will not disappear when you upgrade the operating system—at least, that's been my experience.
iTunes still looks for AppleScript files in this location to make them available in its Script menu, so if your system isn't configured with the ~/Library/iTunes/ folder you will have to create the intermediate "iTunes" folder there and then the "Scripts" folder within it.
AppleScripts can also be installed in the /Library/iTunes/Scripts/ folder—that's the [startup disk]/Library/ folder and putting AppleScripts here makes them available to all Users. Again, the "Scripts" folder may have to be created by the user.
AppleScripts will appear in the system-wide Script menu in the Menu Bar when they are installed in ~/Library/Scripts/Applications/iTunes/ for the single User or /Library/Scripts/Applications/iTunes/ for all Users.