Adding Ticket Number & Custom Field to Ticket Reply Email Subject Line

It would be greatly appreciated it we could add fields to the Subject Line when one of my reps respond to a new ticket. Other systems we have worked with have this functionality and it helps our customers (and reps) track open tickets.

Currently I have to rely on them manually adding it - naturally this causes inconsistencies. A feature like the Personalized Tokens in the Marketing Hub should be available for the Conversation/Tickets.

This feature would be very helpful to automate the ticket number into the subject line of emails when corresponding with users. Where is this on the roadmap?