If what you suggest were implemented, a line item could not be edited to include an inventory or non-inventory item. If you were to accidentally select some other account, your only option would be to deleted the line item and start over.
Imagine that you began entering a line item manually by selecting an expense account. Then you recalled that you had a non-inventory item defined for whatever you entered. You would not be able to select it.
You will not see this implemented.

