More granularity in file names
log the full command if the execution fails, to help diagnose the problem.
Allow %year% %month% %day% %hour% %minute% %second% to be able to build up custom timestamps in output files.
Add %suffix% that would return ".pdf" if filename is "somefile.pdf".

Since these features relate to scripting, all these additional macros can already be extracted with little effort from any scripting language. These additional macro options can be added into the next major version and will not be included in DM2.
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1. When execution scripts or applications fail, the full command is already logged in the Activity Log tab along with the full error message of the failure and stored in the activity logs for later inspection. You can also log all execution data by using "Everything" as the logging level: https://directorymonitor.com/images/features/options_main_logging.png
2. This is simple enough, however, splitting dates in scripts is simple enough as well. We'll include additional macros in the next major release. Refer to this link for a number of solutions on how to get date parts in various scripts: https://stackoverflow.com/questions/3472631/how-do-i-get-the-day-month-and-year-from-a-windows-cmd-exe-script
3. Extracting the extension in a script is also incredibly simple. You can use %~x1 in a batch file, [System.IO.Path]::GetExtension in PowerShell, require('path').extname in NodeJS etc.
For both #2 and #3, if you want to manipulate the file paths or dates using the existing macros available, just wrap your application call in a script or batch file which provide easy options to extract these values.