Ive often thought about this.
No one can deny that some women have good leadership and organisatonal skills, just like some men also have the same type of skills. What you have between your legs is irrelevant.
In my opinion the main problem that could arise from a co-leadership of sexes, is that men and women may start competing with eachother for positions and roles. An 'us versus them' mentality could break out, and could lead to co-operation problems, dissentions etc.
CC