At the moment Using Perl 6 in the section on interpolation has this to say

TODO: explain (non-)interpolation of arrays and hashes once Rakudo 
gets that right
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You are seeing the expected behaviour rather than a bug:
You may see a bug if you attempt, (haven't got access to Rakudo @ work)

my @array = ( 1 , 2 , 3 , 4 );
say "The array is {@array}";
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The {} curly braces within double quotes should allow any expression to be interpolated into the string.