How to extend EE's new routes feature in an extension hook.

ee-route-example.php

<?php

public function core_template_route($uri_string)
{
    ee()->your_lib_or_model->load_routes();
    
    // Rest of your hook processing, if any.
}

public function load_routes()
{
    if (version_compare(APP_VER, '2.8', '<'))
    {
        return;
    }
    
    ee()->load->library('template_router');

    // Load your routes here from config.php or wherever.
    foreach ($routes as $route)
    {
        // Make sure you have everything first
        //      $route being your custom route path
        //      $group_name being the group it is assigned to
        //      $template_name being the template it is assigned to
        if ($route && $group_name && $template_name)
        {
            $template_route = ee()->template_router->create_route($route);
            $route_parsed = $template_route->compile();
    
            ee()->template_router->end_points[$route_parsed] = array(
                'template' => $template_name,
                'group'    => $group_name
            );
        }
    }
}