Ubisoft have released a small preview video of the new Hereford Base, showing what it looks like after Grim Sky facelift. As they previously stated, Ubisoft are remaking the map in order to fit Rainbow Six Siege's competitive bill.
Gameplay issues regarding Hereford Base should be removed with the rework and the map's standards should be up to the challenge of competitive play now. According to Ubisoft, the map should still feel familiar but it will now also contain "many twists and should be treated as a new map", probably meaning not to take it for granted if you had intimate knowledge of Hereford Base's previous iteration.
Speaking of which, the first version apparently served as the first prototype for a Rainbow Six Siege map, which is likely the reason why it got outdated and needed a rework in the first place. Apparently the decision to rework the map wasn't easy as it's not a habit for Ubisoft to rework maps, particularly iconic ones. Then again, just a few lines prior, it sounded a lot like they're intending to go for more reworks in the future.
Either way, the new Hereford Base should have a bigger layout so each floor will have more surface. New staircases will serve to make rotations easier and the map should overall feel the same but different. Same in the sense that the art team worked on preserving the old aesthetic, but new in the way of gameplay.
The devs stated that their level design team has matured over the two years, through adding new maps via new operations, and it was high time to revisit an old one. Apparently, reworking a classic map is a "rare treat", so the team jumped on it with enthusiasm.
Ubisoft have thanked the community for immense amounts of feedback, which made the rework possible. While neither the video nor the blog post reveal too much about Hereford Base's new hairdo, it is likely to include community requested fixes. We will know for sure after the official reveal during the Six Major stream from Paris, at some point from 17 to 19 August 2018.