Enable topic title variable in email notifications subject for new topics

Hi,
Users that are subscribed to a category do not get the topic title in their email subject whenever a new topic is created. 
As seen in the reply by ​@Julian, perhaps this was due to avoiding titles being too long.

Our most active users (without access to Control) would like the {topic_title} variable enabled for new topics, as it would make it easier for them to engage with topics of their interests.