All male gymnasts (no matter how inflexible) try to do el-grip (e.g. eagle) swing on Horizontal Bar.
Every coach has stories about how some super inflexible gymnast (i.e. John Fair) somehow managed to do this skill in a competition. … Personally I wish F.I.G. would put less emphasis on this family of swings.
To test if kids have potential, have them start in a deep pike with hands on a Floor bar. Then jump to start putting weight on the hands.
This flexibility is trainable, but not so much as other ranges of motion.
Gymnastike posted video of Tom Forster assessing gymnasts for el-grip potential at GAT 2010. In my experience only about 1 girl in 10 has both the specific physical potential as well as the general all-around potential to pursue this family of skills. The time is better spent elsewhere, for most.
related – The Gym Press – Vitaly Marinich – Developing the Takamoto
Gymnastics Coaching.com 