#2 and #3 seem reasonable, but are largely out of the local government's control and both are chicken-egg situations. If it was the most profitable use of the space to do mixed retail then developers would, but its not, so they don't. But the city wants mixed use retail because its better for the citizens, and they have the legal authority to force developers to make slightly less money in exchange to improve the city for its citizens, just as they do with any other taxes, so I don't see why they shouldn't. #2 and #3 (and probably #1) should then follow?

#1 is a cop-out. We can't require mixed use retail because none of our developers (who are experts at residential leasing) will admit to having the expertise to do mixed use retail leasing. Its not that different nor is it rocket science.