Not sure if I understand what you're trying to do? If you need to display the sitemap as a part of your site design, why not just use content/view/sitemap/2 for the desired siteaccess?
A quick 'n' dirty solution would be to create a new object of any class and then make a node-specific override template. Another, approach is to create an extension with a separate view. It depends on your needs.
is there no standard solution for this. It isn't anything strange what I am trying to do here is it?
let's take a search form for instance. the website should present a search form. There is no class I need to use so a site editor could create a search form instance.
I create a folder named seach form and in this folder I want to 'create' the form, which consists of only template code.
Your quick and dirty sollution occured to me as well. I could create a class with no fields fos instance, and put my code in a template for this class. However, a standard sollution must be at hand. everybody has these funcitonalities in their sites!