Yeah, most Unix systems have been more or less OK with it since the prior round of Internet-Drafts in 2008. Some more details in the implementation status section in https://datatracker.ietf.org/doc/draft-schoen-intarea-unicas... (which I'll need to continue updating on the basis of more tests).
The situation is more complicated for routers, including high-end datacenter routers. (If you have something that's post-2008 Linux under the hood, it probably works although there might be some higher-level software enforcing special cases.) The trend has been toward more router support for 240/4, but the special case was historically enforced in many devices, and older routers sometimes stay in use for quite a while.
Windows is definitely the outlier on endpoints; when I gave some presentations about 240/4 over the past year I pointed out that, if people were watching them on a device running anything other than Windows, that device would most likely interoperate with 240/4 addresses.
The situation is more complicated for routers, including high-end datacenter routers. (If you have something that's post-2008 Linux under the hood, it probably works although there might be some higher-level software enforcing special cases.) The trend has been toward more router support for 240/4, but the special case was historically enforced in many devices, and older routers sometimes stay in use for quite a while.
Windows is definitely the outlier on endpoints; when I gave some presentations about 240/4 over the past year I pointed out that, if people were watching them on a device running anything other than Windows, that device would most likely interoperate with 240/4 addresses.