The default alignment rules in emacs are meant to handle = assignment not => fat comma.

So task number one would be to separate these cases.

Secondly we need to define region separators.

as a demo: resetting the align-region-separate to handle parentheses helped

(snippet from customize: Align Region Separate: Value Menu Regexp defines section boundaries: [][{}])

to format

$a = {
    bla => 1,
    trax => [
        bla2 => {
            sauh1 => 1666,
            3 => 2,
        },
    ],
    #
    bla => 1,
    trallxa => 2,
};
[download]

to this, hence handling different levels accordingly

$a = {
    bla  => 1,
    trax => [
        bla2 => {
            sauh1 => 1666,
            3     => 2,
        },
    ],
    # new section
    bla     => 1,
    trallxa => 2,
};
[download]

but this doesn't help with this because the separators will be inside each line

my $h_periods = {
    Mercury => { orbital => 0.24, rotation => 58.64 },
    Venus => { orbal => 0.62, rotation => -243.02 },
    Earth => { orbital => 1.00, rotation => 1.00 },
    Mars => { orbital => 1.88, rotation => 1.03 },
    Jupiter => { orbital => 11.86, rotation => 0.41 },
    Saturn => { orbital => 29.46, rotation => 0.43 },
    Uranus => { orbital => 84.01, rotation => -0.72 },
    Neptune => { orbital => 164.8, rotation => 0.67 },
};
[download]

The only way to solve this is to use indentation to distinguish groups.

According to the docs it's possible to use a function call back instead of a regex, but documentation is sparse.

I wanted to document my findings before getting lost in other projects ... ;-)