Board Thread:New Features/@comment-26180812-20180918201309/@comment-27345308-20180918201523

Discussions FAQ says:

We have no immediate plans to add a "sticky" function. We'll be examining the types of content that admins post and want to "sticky" in Discussions, so please send us examples of such posts. It’s important to acknowledge that on traditional forums, many readers will skip over sticky threads. Posts are often stickied at the top and rarely unstickied, resulting in a large stack of posts to scroll through before you even see newer content. That being said, Special:Contact/feedback is the right place for this.
 * Will there be "sticky" function in the future, to pin posts at the top of the post list (or a category view)?