I've made #4 work finally:

while prompt qq/Please input a number (>1):\n/ -> $_ {
                say $_;
        }
[download]

A lot of unexpected things:

1. For some reason, Rakudo does not recognize the "LOOP:" construct, I just can't use "goto LOOP" to jump to a label.

2. The simple "while(<>){}" idiom doesn't work anymore. Though I've heard that "for =<> {}" is one alternative, but it seems that Rakudo doesn't support it yet.

3. The compiler suggest me to use "lines()" instead of "while(<>)", but "lines()" slurps all the input, so I can't input line by line, luckily there is a "prompt" function instead.

4. Since "while(<>){}" does not work, the implicit variable is not assigned, so I have to explicitly assign it by: "-> $_".

5. For some reason, bare function "chomp" and "say" does not work any more, I have to pass the parameter "$_" explicitly.

6. But the chomp function is not necessary anymore, the NL is automatically chomped. This sounds like the "perl5 -l" option, I guess we will need a "perl6 -L" option to do the inverse in the future?

I am surprised that Perl6 is so much different from Perl5.
But the code does become much shorter and clearer, at least from this example.