Does one have to be a Sikh to join the Khalsa? I can imagine "Mohammad Singh" or "Mata Teresa Kaur"... When the Khalsa takes rule and ushers in Satya Yuga, Guru Nanak says that there will be one religion - the Khalsa (in Rajnama and Karninama). Sikhs have respect for all faiths, and I feel that the Khalsa isn't just beyond caste, color, gender, or sexual oreintation, but is also beyond religion.
The Khalsa is a thin path to follow of righteousness and being a sant-sipahi (warrior-saint), but it isn't restricted to Sikhs.
What do you the Khalsa Panth yourselves think?