I would really celebrate any historical layouts of the Ring which are sadly no longer in existence in real life.
Like for example the above mentioned Südschleife (south loop), shown in faint grey in the following graphic and used from 1973 to 1982.
Sadly I’m not old enough to have seen races there live myself but my first experience of watching motorsport at any track was at the Nürburgring ‘Betonschleife’ (concrete loop) marked in red in the graphic, a neat short track similar in nature to Brands Hatch Indy layout and obviously something I would love seeing in Forza just to relive my youth. For orientation: The start/finish line of the Betonschleife is roughly at the same spot as today’s start/finish line of the GP circuit, the Betonschleife was also the connection between the north loop (Nordschleife) we have in game already and the no longer existing south loop (Südschleife), making it possible to combine all three layouts into one gigantic long circuit.
Two more recent YouTube videos document the current state of what is left of the Südschleife. This one includes a useful map overlay:
And this one includes some historical photos as well:
