As Facebook continues to push ahead with Facebook Stories, and encouraging Stories use, it's trying out a new option which will enable users to share events they're interested in to their Story, where their connections will also be able to register interest for the same, right from the Story screen.

The new function - which is being tested in the US, Mexico and Brazil - will appear on the event page itself. When you tap on the 'Share to Story' option (within the share options for an event), you'll be able to create a dedicated Stories frame, with an event sticker, as shown in the second image above. From that sticker, your Story viewers can register their interest in the same, and you'll be able access a list of friends who plan to attend the event, helping you co-ordinate your attendance.
The sticker itself looks a lot like Instagram's recently added 'Question Sticker' for Instagram Live, which adds a more professional looking way to answer audience queries, as opposed to simply responding to questions submitted in the comments.

That appears to be a focus for Facebook more broadly in 2019 - adding new ways to better integrate different functionality into its live-streaming and Stories options to make them more engaging - though there still seems like quite a bit of room for further customization of such tools.
The addition is also the latest in Facebook's ongoing efforts to encourage Facebook Live use. Facebook has repeatedly stated that Stories are the future of social sharing, and it seems as though the company is determined to make that true - whether through organic usage trends alone, or by force.
Indeed, despite Facebook Live still not seeing significant usage, in broad terms, Facebook continues to add in new tools and options to try and encourage users across - and they even appear to be using some questionable tactics and tricks to boost Stories viewer numbers.
For example, if you check Facebook on your mobile, you might see that a friend has added to their Story, signified by the blue circle around their Stories image along the top bar. You tap on it, check it out, move on. If you then open Facebook on desktop, that same friends' story will likely appear with a blue circle again, which seems to indicate that they've added to their Story since you last checked. Click on the Story and you'll see the same frames, nothing new.
Now, it's possible that this is just a communication issue between the desktop and mobile apps, but it may also be a way to boost Stories usage figures. Now, you've tapped on Stories twice in a day, doubling your potential interest, while also adding to the overall time spent within Stories. A second here or there may not count as 'meaningful engagement', but if every one of Facebook's 2 billion users spent an extra second, that might shift usage numbers in a significant way.
Why Facebook seems so intent on making Facebook Stories a thing is hard to say - for one, overall engagement on Facebook is reportedly down across the board, especially among younger users. Maybe Stories is a way they can counter this - Stories also enables Facebook to share it's AR tools, which they could see as a way to slowly shift users into the next phase of social sharing, which likely involves full VR, some time in future.
Whatever the reason, Facebook is still very, very keen for you to try out Stories, and will continue to add new options like this to entice more people to it.
In other Stories news, Facebook is still working on its links in Facebook Stories test, with some users noting that they did have the function, but it's now gone.
But Digiday reports that there's now another way for brands to use this functionality - via Instagram-style swipe-up links:
"This swipe-up feature is available if a Facebook Page owner has a verified Instagram account and cross-posts their Instagram Stories that have swipe-up links to Facebook Stories. A Facebook spokesperson said the company will soon test the ability for Facebook Pages to share links organically in Facebook Stories."
This also comes as Facebook tests it's CTA Stickers for Page Stories, another way for businesses to drive more direct response

The capacity to drive direct action, particularly traffic, will be a big lure for brands - another key element which may attract more businesses to the option.