<?php
function array_key_camelize($array)
{
    $result = [];
    foreach ($array as $key => $value) {
        $result[camelize($key)] = is_array($value) ? array_key_camelize($value) : $value;
    }
    return $result;
}

function camelize($str)
{
    return preg_replace_callback('/[_-]([^-_])/',
        function ($m) { return strtoupper($m[1]); },
        $str);
}

$array = [
    'this_is_snake_case' => 'this_is_snake_case',
    'this-is-kebab-case' => 'this-is-kebab-case',
    'nest' => [
        'this_is_snake_case' => 'this_is_snake_case',
        'this-is-kebab-case' => 'this-is-kebab-case',
    ]
];

var_dump($array);
var_dump(array_key_camelize($array));