Assets folder first level open by default
You could modify this JavaScript to do it for you. We currently have it running on a site where this was sought-after

Caveat: Our script opens ALL folders, not just the first level - hence the need to modify.

jQuery(window).on('load', function() {
    var $ = jQuery;

    var openFolders = function() {
        var imageRootLinks = $('a[data-key^="folder:"]');

        $.each(imageRootLinks, function(index, link) {
            var imageRoot = $(link).parent();
            var toggle = imageRoot.find('.toggle');
            if (toggle.length &amp;&amp; !imageRoot.hasClass('expanded')) {
                toggle.first().click();
            }
        });
    };

    // open folders in left menu
    openFolders();

    // open folders in image selector
    $(document).ajaxComplete(function(e, status, requestData) {
        if (requestData.url &amp;&amp; requestData.url.indexOf('getElements') &amp;&amp; requestData.data &amp;&amp; requestData.data.indexOf('context=modal&amp;elementType=Asset') != -1) {
            openFolders();  
        }
    });
});


Then simply include the JS-file through a plugin

// runs on all requests
public function init() {
    // check that user is logged in and in the control panel
    if ( craft()-&gt;request-&gt;isCpRequest() &amp;&amp; craft()-&gt;userSession-&gt;isLoggedIn() ) {
        // the includeJsResource method will add a js file to the bottom of the page
        craft()-&gt;templates-&gt;includeJsResource('myplugin/js/openFolders.js');
    }

}