sarbat khalsa is a congregation of all... and whatever they decide is the rule.... now if we add up decision of all sikhs regarding their hairs( I am not going by SGPC /political definition of sikhs)... we should all agree that cutting or keeping hairs does not really matter....
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-youth/22759-hair-and-general-sikh-philosophy-study.html
personally , Tenth guru ji ordained it for khalsa ... and not for all sikhs......Khalsa panth within sikh religion.