Using mRNA as a New Basis for Heart Repair?

I read an interesting article, on Science Daily, on a new research of heart repair, mainly after a myocardial infarction, using synthetic mRNA.

Scientists at Karolinska Institutet and Harvard University have taken one step closer to finding a new way for the heart to repair itself. Instead of the traditional way of introducing new cells into the heart to build cardiac muscle, this new way explores injecting the heart with synthetic mRNA to trigger the native stem cells in the heart to start making new coronary vessels as if it were a fetal heart all over again. 

This seems like a great, new way to help victims of heart attack if it proves to be successful, but of course it is still fairly new with many downsides:

1. It has only been tested on rats

2. They are just now moving towards testing it on other animals

3. Until it is tried on a human, scientists will never know exactly how well it does or does not work for the ultimate target species

4. A specific catheter is still trying to be made for perfect injection

5. The injection must be done within 48 hours of the heart attack to be successful

6. The injection will not work unless it is injected exactly in the location of the heart progenators 

7. Very specific synthetic mRNA must be made to be able to hide from the immune system

With currently more cons than pros, would you say the researchers should continue moving forward? If so, what other tester animals would you use to dodge ethical/moral concerns? Also, how should they go about testing it on humans once they get to that stage?

Link to article on Science Daily