1) Change the Target Test Case selection from a drop-down single-selection list box to a sub-dialogue that allows multiple Test Cases to be selected and test steps to be selected for each test case. 70% of the time I spend in ReadyAPI is repetitive data entry of cloning assertions one at a time between test cases where the default test case is the one I'm using for the source.
2) Change the default selection of the Assertions from none selected to all selected. No one ever needs none cloned, that's a non-operation.