Hello Stephan.

You can't use this option out-of-the-box, but there's a way to do it.

You need to open this file: ../wp-content/plugins/wpdatatables/templates/admin/table-settings/table_settings_block.inc.php and around line 348 you'll see this:

<select class="form-control selectpicker" id="wdt-rows-per-page">
   <option value="1">1</option>
   <option value="5">5</option>
   <option value="10">10</option>
   <option value="25">25</option>
   <option value="50">50</option>
   <option value="100">100</option>
   <option value="-1"><?php _e('All', 'wpdatatables'); ?></option>
</select>

You can replace the last option (All) with the 1000 option, like this:

<select class="form-control selectpicker" id="wdt-rows-per-page">
   <option value="1">1</option>
   <option value="5">5</option>
   <option value="10">10</option>
   <option value="25">25</option>
   <option value="50">50</option>
   <option value="100">100</option>
   <option value="1000">1000</option>
</select>

 And you'll have that option in the "Display" tab above the table:

Then, open ../wp-content/plugins/wpdatatables/source/class.wpdatatable.php and around lines 3647 and 3650, and replace "All" with 1000, so it looks like this:

$obj->dataTableParams->aLengthMenu = json_decode('[[1,5,10,25,50,100,1000],[1,5,10,25,50,100,1000]]');

And the last thing to do is to go to line 542 of the same file, and modify it so it looks like this:

public function setDisplayLength($length) {
        if (!in_array($length, array(1, 5, 10, 12, 20, 25, 30, 50, 52, 100, 200, 1000))) {
            return false;
        }

So, again, replace -1 with 1000.

You may also want to add the value in ../wp-content/plugins/wpdatatables/templates/admin/table-settings/column_settings_panel.inc.php around line 570, if you wish to add that value to possible column options (if you have a select-box filter or selectbox editor input type, this would be the number of values displayed in those drop-downs):

<div class="form-group">
                                    <div class="fg-line">
                                        <div class="select">
                                            <select class="selectpicker" id="wdt-possible-values-ajax">
                                                <option value="10">10</option>
                                                <option value="25">25</option>
                                                <option value="50">50</option>
                                                <option value="100">100</option>
                                                <option value="-1"><?php _e('All', 'wpdatatables'); ?></option>
                                            </select>
                                        </div>
                                    </div>
                                </div>

Please make sure to delete the cache in your browser after you apply the changes.