Wine-Mono Won't Bother With .NET 5.0 - The Official Microsoft Binaries Should Work Fine
Microsoft announced on Tuesday that the .NET 5.0 release is now "feature complete" for this major overhaul of .NET that breaks compatibility with prior versions. Microsoft .NET 5.0 has many changes to its libraries and runtimes, introduces WebAssembly support, support for single file applications/executables, new APIs, better performance, and much more.
While normally new .NET releases are a major pain for the likes of Wine in trying to support Windows .NET applications on Linux and other platforms, the .NET 5.0 milestone shouldn't be such a pain point.
CodeWeavers' Esme Povirk has shared that the official Microsoft binaries of the .NET 5.0 preview images should already be working fine on Wine.
Due to .NET 5.0 already working on Wine and itself being largely open-source, they will not try to extend their existing Wine-Mono package to support .NET 5.0 or to form any new open-source reimplementation.
Since .NET 5.0 breaks compatibility with earlier versions (winforms has removed APIs and changed the default font which breaks some application layouts), is open source, works independently from .NET 4.x and earlier, already works in Wine, and has a build system very different from the one used in Wine Mono, it does not make sense to try to replace it with Wine Mono. Should Wine require any changes that upstream does not wish to merge, we will need our own fork, otherwise we can simply use the official binaries.
So at least for now it's looking like .NET 5.0 will be playing nicely on Wine, albeit using the official Microsoft binaries.
Those curious about all the changes coming with .NET 5.0 can see the Microsoft Developer Blog. The official .NET 5.0 release is expected by November.