Currently, this block exists:
I am suggesting the below block be added, or maybe even replace the above block altogether:
The first dropdown may be either [ or (, and the second dropdown either ] or ).
Here is an implementation using My Blocks+ and Dropdown Maker:
When both dropdowns are in the "closed" state, it would function identical to the is (x) between (m) and (n)? block, except for the case where m > n, in which case the interval block would always return false, whereas the between block would swap m and n and continue as normal.