i18n::
  * Mark strings for translation in `system-upgrade-redhat.c`

Docs::
  * man pages like whoa
  * document boot args (rd.upgrade.*)

Improve progress reporting::
  * change /etc/*-release so "Welcome to XXX" message says "Welcome to redhat-upgrade-tool"
  * count %posttrans scripts, take %posttrans into account for upgrade progress
  ** although actually posttrans is only like 1.3% of elapsed time...
  * warn user about long-running %post scripts
  ** in a perfect world the scripts should do that for us
  * use RPMCALLBACK_*_PROGRESS for finer-grained progress
  * invoke a callback during pre-transaction RPM header scanning
  * Fancier plymouth theme

Error detection / reporting / handling::
  * Fail if some packages are missing
  ** Allow override via commandline arg?
  * Add a 'upgrade-failure' callback (for e.g. restoring a backup)

Upstreaming::
  * get 90system-upgrade upstream
  * get save-initramfs.sh into upstream dracut

Backup/restore::
  * If possible, take LVM/btrfs snapshot before upgrade
  * On failure, restore snapshot