automatically quoted strings [...] more or less matching /^([1-9]\d*)|([a-zA-Z_]\w*)$/

No, it doesn't match numbers at all. If => autoquoted numbers, the key would be a bunch of 9s in the example below. Non-strings (numbers, references, etc) are converted to strings (although I think there is planned change to preserve the type of the key, maybe in perl6), but that's not the same as quoting. I think that means that if and only if it's a valid subroutine name, it'll get autoquoted.

>perl -le "
   %a = (999999999999999999999999999999999999 => '');
   print keys %a";
1e+036

>perl -le "
   %a = (999999999999999999999999999999999999, '');
   print keys %a";
1e+036
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