TOWUK_ru there are reasons for which this is not desirable for performance, as well as creating a huge conflict management requirement against other extensions.
If you want to register custom pages with custom URLs, you can use the Flarum extension API to register your own pages. It's not that difficult and doesn't even require the use of the database.
What we could maybe do is provide an extender that allows to alias a page to a custom URL in the local extend.php. This avoids the performance issues (loading the list of pages before the router) and leaves the admin to manage possible conflicts themselves.
