I just bought F1-F4 and I am stoked! However, I think it would be useful to have common names for the exercises in addition to the official names. For example, I find it more useful to think of "old cow/angry cat" instead of "FL/PE1>iM" and "elbow plank" instead of "sPL/PE2" when I am about to exercise. Therefore, one suggestion for improvement is to add such common names for all the exercises in the book.
Sometimes, there are several common names. For example, I did not know until recently what a side lever (SL) is. But I heard of the "human flag". The full SL is in F4, I guess, but even F1 has some exotic exercises! :-) Other times, there are perhaps no established common names. But that's ok. Maybe we can be creative? What do you think?