Apple has today released its guidance notes for system administrators, to help them prepare for the release of Mojave, now expected in September (although Apple has not announced any date yet): this support note contains details released so far.

Of significance to many other users will be:

• Those using Proxy Automatic Configuration (PAC) with FTP and URL schemes must change to HTTP and HTTPS schemes, whether set in System Preferences or in a profile. FTP and URL schemes for PAC will no longer be allowed.
• Using the kickstart command to enable remote management will only allow you to observe it when sharing its screen. If you want to control a remote Mac, you must enable remote management in System Preferences.
• Macs with T2 chips will not start up in Single-user mode when using either Full Security or Medium Security for Secure Boot, but will still have access to Recovery mode. Only the No Security option will boot in Single-user mode.
• Symantec CAs will be completely distrusted in the autumn/fall, and the Federal Common Policy Root CA is being removed from the macOS Trust Store.

(Thanks to @mikeymikey for drawing attention to this.)