Thank you for your post. The closest replacement model for the MB973SP-B is the MB830SP-B (https://www.icydock.com/goods.php?id=300). While the MB830SP-B does not have doors, it does support the same amount of drives and fits in the same space as the MB973SP-B.
The decision to discontinue the MB973 series was made by headquarters. Unfortunately, I do not have additional details on the discontinuation of this series.
If you have any questions on our products, feel free to send a message or send an email.