The next version of ASP.NET is 4.5. The official information is at http://www.asp.net/vnext.
There are two ways to experiment with ASP.NET 4.5 beta. The first is to install Visual Studio 11 beta. The second way is to install ASP.NET MVC 4 beta on Visual Studio 2010 to experiment with a subset of the features. Visual Studio 11 beta contains .Net Framework 4.5 beta. .Net Framework 4.5 is a highly compatible in-place update of .Net Framework 4.0. If you uninstall .Net Framework 4.5 beta, you will have to reinstall .Net Framework 4.0. For this reason, I would suggest you to experiment with Visual Studio 11 beta on an experimental machine, perhaps on a Windows 8 consumer preview VHD.
On the other hand, ASP.NET MVC 4 beta consists of a set of new assemblies that can run side-by-side with MVC 3. It also has a new set of templates for MVC 4 projects. The only thing that affects MVC 3 work is that it changes the intelligence for web pages (.cshtml and .vbhtml) to support web pages 2 features. You need to build your web application before you edit any .cshtml or .vbhtml pages to overcome a bug.
The following features can be experimented with ASP.NET MVC 4 beta on VS 2010:
Not part of ASP.NET MVC 4 beta, there is an exciting open source framework from the ASP.NET team called SignalR that be experimented in VS 2010. SignalR allows developing long polling Comet type of applications using .NET. The ASP.NET team has also created an open source chat application called JabbR as a case study.
In future blogs, I will blog my experiment with each of these exciting new areas.