Drush command that creates a new update script

Add a new drush command (e.g. drush updatescripts-create "your-fancy-updatescript"). The command will create a new empty (or with a simple template) updatescript in the appropriate directory with the "next best number" as prefix.

drush updatescript-create "your fancy updatescript" or
drush usc "your fance updatescript"

creates a php file in /sites/default/updatescripts/ (or in the appropriate directory for multisites) with the filename
[NEXT-BEST-NUMBER]-[ARGUMENT].php

Maybe you can use the drush argument for the file name also for the updatescript description.