We made this change because the old design was too subtle: most of our users never even discovered the Trash feature, which was a really pity.
Now, the Trash column will automatically display whenever it has anything in it. We are using lazy loading for the Trash, so performance is not affected for people who have very large Trashes. (Some people, who have been using the same board for years, have hundreds or even thousands of items in their Trash.)
If you don’t want to see the Trash, you can hide it using the Filter button that appears on the top right of each board: