What version are you running?
2.5.8
What's the URL of the page this enhancement relates to, if any?
NA
Describe the enhancement and the motivation for it.
To allow modifying notification email subject
What operating system are you using? What browser?
Ubuntu 14.04
Please provide any additional information below.
In release 2.5.8, it has this feature:

TemplateHook now supports the review-email-html-summary and review-email-text-summary hook points for adding custom content to HTML and plain text e-mails (respectively).
It would be great if it supports updating the review email subject as well.