Hi
I am really missing this feature myself and ended up using a helper like yours in my latest project. Unfortunately, I don't think you can access the index in Mustache.
Handlebars has an easy access without any helper using {{@index}}. Hopefully the CanJS team can implement it into the canjs mustache template?
From Handlebars homepage:
{{#each array}} {{@index}}: {{this}} {{/each}}