The thanks extension currently allows users to thank other users for edits. It should also be possible to thank other users for articles they created. I see two possible UIs for this:
First, add a thank button to Special:NewPages
This has the drawback that unexperienced patrollers may thank users for vandalism/spam.
But on the flip side, it may help in editor retention.
The other way could be to add a thank button at the bottom of the page alongside the [Mark this page as patrolled] button.
This would help patrollers to verify that the article is not spam/vandalism, and then users can be thanked on the click of a button.
As of now, thanking users for their creation of the article (i.e first edit of the article) is possible, but for that one has to see the page listed at Special:NewPages, then open the article to see if its vandalism/spam or an actual article, then go to the history of the page and click the thanks button.
It'd save a few pageloads if the thanks button was more easily accessible.