This might make sense as a transcludable special page (and may depend on T117142).

If we model it off of the Python script I wrote for WikiProject X:

Each entry is for when a new section is posted to a talk page, i.e. an edit to a talk page namespace with the edit summary "new section". The newest ones are on the top. Thus each entry is not for each line of conversation to transpire on a talk page, but for when a new discussion is posted.

The current implementation posts the listing to a subpage called /Discussions. This page lists 15, with the bot chopping off the oldest entries to ensure that no more than 15 are ever listed. When this subpage is transcluded, only 4 show up, with a link to view more. If we are re-implementing this as a transcludable special page, I recommend the number of conversations showing up to be a custom parameter, with no limit otherwise imposed. Depending on what is feasible for MediaWiki.

The "population" of talk pages to feed from is based on a database pairing talk pages and WikiProjects, generated by this script. This custom database is used by several other scripts as well. The database exists because WikiProjects are inconsistent in their categorization of WikiProjects, requiring a lot of work to capture each use case, and rather than do this each time a script runs, I have the script run daily to generate the database. T117142 would obviate the need for this, as would English Wikipedia being totally consistent in its WikiProject categorization scheme. We could create a general special page for new discussions anywhere on Wikipedia, with a further option to subdivide by category (e.g. Special:NewDiscussions/Category:WikiProject_Chemistry_articles).

@kaldari, if we go the transcludable special page route, while having T117142 in place would be nice, I don't think it should be a blocker by any means. Categories would be good enough; it would encourage WikiProjects to be consistent (or for those large projects that want differentiated discussion feeds, a category-based system would allow that).

Could this be a database table (with accompanying special page) akin to the recent changes table? Or as a column on the recent changes table? This table (or column) would be populated based on saved edits to talk pages with &section=new parameter. A fancier approach would look to see a new section created at the bottom of a talk page, since people like to create sections by editing an existing section on the bottom of the page. (For WikiProject X, we conveniently pretend that people don't do that.) You may also want to keep Flow boards in mind, but I imagine Flow is better at indicating when new sections are created.

From there, we could generate lists of new discussions by intersecting the new discussions table with the table from T117142 (or any category, for that matter).

I think this would be a useful module for WikiProjects. I've been tempted just to manually create a list of the newest WikiProject-wide topics (editorialized to keep out not-so-useful ones), but I would probably have to update this on a daily basis. Is there any way to create such a list with any current wiki technology outside of my using RecentChangesLinked on a list of talk pages and plus cut-n-paste of topic title/links?