Why couldn't you create a program that recognise a certain structure (such as the structure of a for loop) and convert it into the gui for loop? Yes you can. It's just not going to be easy to make the thing flexible, and probably nearly insane to make a "deconverter" work properly in the first place.
If you can convert plastic in metal, you can convert metal into plastic as well.
Sure, I understand your point of view and you can't possibly convert a jass trigger in 100% gui (unless perhaps if the trigger was originally made in gui), but that's not what he asked. He asked if it's possible to reproduce certain jass parts into gui, and yes, theoretically it is.
But practically, nobody is going to consider doing it, especially because it would probably be easier just to teach you jass.