The .NET platform will become unified around the .NET Core standard. While .NET Framework 4.8 has just launched with Visual Studio 2019, .NET 5.0 will be the successor to the upcoming .NET Core 3, and its line will become the whole of .NET. Every year, a new version of .NET will launch in November. Every even-numbered version of .NET will be an LTS build, which means that you should target the even-numbered APIs (such as .NET 6, .NET 8, .NET 10, and… uh… .NET 3.1…) for bug fixes without breaking changes.
As far as I can tell, Microsoft has not clarified whether .NET Framework might see a version 4.9 (or more) before the sunset. .NET 5+ will be the future, however. .NET Framework will eventually yield to the .NET Core, now just .NET, line at some point in the .NET Framework 4.x lifecycle. If this branding seems a little confusing – it’s to make it easier in the future.
As for the features? .NET Core 3 was already pushing to allow targeting Windows Forms, WPF, and other frameworks (ex: Xamarin). The main push in .NET 5 will be interoperability with other languages, such as Java, Objective-C, and Swift. They will also focus on ahead-of-time (AOT) compilation, because why not make applications coded in statically typed languages faster and deploy smaller?
Seriously, why not?
.NET 5.0 is expected to ship in November 2020, one year after .NET 3.1 LTS (November 2019).