Snippet for namespaced SilverStripe Pagetypes to find their controller in a different namespace.

Page.php

<?php

namespace App\Project\Model;

use SilverStripe\Core\ClassInfo;
use SilverStripe\CMS\Model\SiteTree;
use App\Project\Control\PageController;

class Page extends SiteTree 
{
    /**
     * Returns the controller class for this page. If a subclass of the page
     * controller exists, use that. Otherwise default to the base namespaced
     * controller.
     *
     * This is required as the SiteTree getControllerName doesn't handle cross
     * namespace (i.e \Model\ vs \Control).
     */
    public function getControllerName()
    {
        $current = static::class;
        $ancestry = ClassInfo::ancestry($current);
        $controller = null;

        while ($class = array_pop($ancestry)) {
            if ($class == self::class) {
                break;
            }

            if (class_exists($candidate = sprintf('%sController', $class))) {
                $controller = $candidate;
                break;
            }

            $candidate = sprintf('%sController', str_replace('\\Model\\', '\\Control\\', $class));

            if (class_exists($candidate)) {
                $controller = $candidate;
                break;
            }
        }

        if ($controller) {
            return $controller;
        }

        return PageController::class;
    }
}