Impossible to execute a fully custom Template/Template content

From caubin:

I found out that the InternalTemplateManager does a cast from a TemplateContent to a DefaultTemplateContent which is a private class here : (https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-oldcore/src/main/java/com/xpn/xwiki/internal/template/InternalTemplateManager.java#L739). Could it be possible to make this class public in order to extend it later ?

Right now, we can't really extend the Template class if this cast throws an exception every time we call templateManager.execute(myCustomTemplate)