This would be incredible!
I think it’s in line with the intention of tags being lightweight while acknowledging the fact that in order to keep a forum organized, people need to have the same definition of what a tag means and when to use it.
I think having a hidden long description could still be helpful to do things like explaining the criteria for how to use a tag. Who can add this tag? Does a parent tag need to be added as well to use this tag? Perhaps this would be particularly helpful for staff.