You can use a Hero Attribute tile to display any attribute reported by your platform’s weather device.
For example, it looks like the weather device I’m using with SmartThings reports a pressure attribute which includes the barometric pressure and direction:
I’ll leave this thread open for others to vote on as well. We’ve had feedback that there’s too much information displayed on the weather tiles already, so we’ve been hesitant to add more to the tile.
A key part of how we prioritize what we work on is community feedback, so if enough people share the interest in adding pressure to the weather tile, that helps get it bumped up the list! 
That being said, there’s a fairly straight forward way to accomplish this with Hero Attribute tiles as shown above.
A popular approach to weather is to use Media Tiles to integrate weather from your favorite sources. You can find more information in the Weather Tiles help article or by searching this community for ‘weather’ - for example, the Weather Sources thread is popular