The following is not allowed by the ES6 grammar:
function foo(...[a]) { }
var [...[b, c]] = [0, 1, 2];
The relevant grammar production is:
BindingRestElement[Yield, GeneratorParameter] :
[+GeneratorParameter] ... BindingIdentifier[Yield]
[~GeneratorParameter] ... BindingIdentifier[?Yield]
And a BindingIdentifier does not include a binding pattern.