ASP.NET MVC 4 is being talked about now, as it's been over a year since MVC3 came out. Microsoft has released the ASP.NET MVC 4 Roadmap, which gives some hints as to the functionality to come in the newest version. It's obviously not concrete, as things can change during development (as we all know) but it's a pretty good indication of what to expect.
Microsoft are integrating heavily with HTML5, Mobile devices and the cloud, as well as making everything and little bit more efficient and a little bit smoother. That seems to be the summary of their plans for ASP.NET MVC 4.
I'm just going to walk through some of the features that are mentioned:
Recipes
This sounds pretty interesting. It basically sounds a lot like jQuery plugins, but for .NET MVC. In a normal situation, this isn't particularly easy to do. Things like AJAX grids, for example, often involve some front-end markup, some back-end code (including data binding and data access). What recipes do is give you a nice, simple way of adding a "plugin" to your project. It automatically generates all the required code for you. This could potentially be a very interesting development, as it would allow easy creation/exchange of MVC "plugins" that you could use to quickly implement complex functionality with minimal work.
Default Template changes/New mobile template
Mainly to do with mobile support, from the looks of it. Detection for mobile devices will be added for the default "MVC site" template to avoid all of the awkward zooming in/out that you need to do to navigate the default site at the moment. It gives you a nice base to build from. Also mentioned is a new "Mobile Application" template, which will integrate with jQuery Mobile and allow you to optimize for mobile and tablet devices. MVC may also implement "mobile-specific views", which the application itself would handle, ensuring that mobile users get a more specifically designed experience.
Integrated CSS and JavaScript bundling
This functionality will allow the application to consolidate multiple CSS stylesheets and JavaScript files into single files, and reduce the size of the final file by removing whitespace and comments and so on. There's already ways of doing this at the moment, but this would come as standard, so you wouldn't even need to worry about it. Could be a nice feature.
All in all, sounds pretty cool, and I'm looking forward to messing about with some of the new features when it's released.