Feature summary (what you would like to be able to do and where):
A user opening a thread / topic on any of available discussion views where Subscribe feature is used, shall be automatically subscribed to the thread on submitting the post.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Originally opening a discussion on various discussion pages a user was expected to add the page to their watchlist to be notified of replies or actually all changes to the watched page. The addition of the Subscribe feature is a welcome change that allows for a more fine grained control over the notifications originating from discussions.

Yet currently opening a topic / thread does not automatically subscibe its initiator to it. And to properly take advantage of the granularity a user needs to take yet another action of subscibing to the initiated discussion.

Benefits (why should this be implemented?):
Autosubscibing to a thread is a natural choice, since rarely anyone speaking out would not like to hear back. This is in nature a DWIM feature.