Some obvious limitations for this pose: hip flexibility, hamstring length (to some extent), arm length (hahahahaha t-Rex arms), and, very importantly, wrist flexibility. Also fear.
The wrist flexibility is a big thing, actually. If you look at the angle of the wrists in this pose (and in many arm balances), the wrists are massively extended (even hyperextended). Students often complain of sore wrists when doing yoga, and especially when a class is focusing on arm balances. It's extremely important that we look after our wrists, and, in the same breath, look after your shoulders, too! I have some lovely (read: torturous) exercises to build 'wrist'strength, as well as some funky stretches to do. I'll probably share those in an upcoming post. Or you can just come to one of my classes ;)