Blandt (and supporters of this useful improvement suggestion),It'll be nice to have an exclude option where users can exclude certain threads and entire categories when clicking the what's new button.
Just like the subscribe to this thread or follow this post, something to exclude would be nice as well
In relation to your suggestion I have put up this one: Sort functionality for What's New. I miss the dedicated forum name-column that vBulletin 3.8 came with, but by providing us with Sort functionality for the 'What's New' we don't need a column. Sorting abilities will make the What's New overview more useful, as does your suggestion. http://xenforo.com/community/threads/sort-functionality-for-whats-new.9603/