I'm currently testing a new special "rapid debug mode" that will allow you to compile and run your app in one or two seconds (or even less). This is a quite complicated solution and I'm still not sure that it is feasible...
The actual code execution speed will be different than a real app as some of the code will be faster and some will be slower. I believe that for most apps it will be fine.
Assuming that all goes well it will make our "development lives" much better