The signs are quite good that Big Sur will also install on somewhat older Macs that Apple has refused to support officially. The way to do this is, as usual, a patch. Currently, the beta version of Big Sur macOS 11 can be installed on machines that are several years older than officially supported by Apple.
The patch can be found here at parrotgeek, who is working on this software solution together with dosdude1, who already brought us the patches for Mojave and Catalina. The currently possible hardware for Big Sur can be seen in the following list (including the restrictions):
As you can see, the computers are all a few years younger than those for which Apple draws the line (see cover picture). This does not mean that older ones, on which you could install Catalina or Mojave for example, are not completely out of the game. This is being worked on diligently. Also on the WLAN support, which is not really available yet.
But if you have ever worked with the Mojave or Catalina patcher, you will notice that the developers are doing an excellent job – and that completely free of charge just for us. So enjoy the benefits you get, but always be grateful.
