Here's a less than satisfactory, but never the less, working work-around:

#! perl -slw
use strict;
use 5.010;
use threads;
use threads::shared;
use Term::ReadKey;


sub readline_NB {
state $buf;
    my $timeout = shift;
    my $rv;
    my $chr = ReadKey( $timeout ) // '';
    if( $chr eq chr(13) ) {
        $rv = $buf;
        $buf = '';
        return $rv;
    }
    else {
        $buf .= $chr;
        return;
    }
}

sub thirdThread {
    printf "[%d] Third thread started\n", threads->tid();
}

sub secondThread {
    while( 1 ) {
        sleep 2;
        printf "[%d] Going to start a new thread\n", threads->tid();
        threads->create( \&thirdThread )->detach;
    }
}

threads->create( \&secondThread )->detach;

while( 1 ) {
    if( my $input = readline_NB( 0.1 ) ) {
        print "CMD: ", $input;
        last if $input eq 'quit';
    }
    else {
        Win32::Sleep 0.1;
    }
}

__END__
c:\test>junk48
[1] Going to start a new thread
[2] Third thread started
[1] Going to start a new thread
[3] Third thread started
CMD: fred
[1] Going to start a new thread
[4] Third thread started
[1] Going to start a new thread
[5] Third thread started
CMD: bill
[1] Going to start a new thread
[6] Third thread started
CMD: quit
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