MVC4 has a great potential for developing RIA applications..
I know that jQuery is most popular js framework and it has a lot of plugins but wouldn't it be a cool thing to have one unified framework for most things (look at dojo uis)?

So my suggestion is to add support for dojo toolkit, and create special helpers, validators, etc.
It shouldn't be hard, cause dojo supports html5 params and with that it's even easier to add unobtrusive validation than in jQuery.. just parse page and it magically works!

What do you think about that?

ASP.NET MVC 3 before, JsonResult use JavaScriptSerializer, JavaScriptSerializer have "Date" format problem.

ASP.NET Web API use Json.Net, the ASP.NET MVC 4 can use Json.Net by JsonResult?

There is a serious flaw with how the unobtrusive library works. A user can't do the following api call because it just doesn't work.

I'm not the only one who has had problems with this....

$.validator.setDefaults({ onkeyup: false });
http://www.tigraine.at/2011/08/26/jquery-validate-and-microsofts-unobtrusive-validation-dont-play-well-together/

http://stackoverflow.com/questions/8022695/asp-net-mvc-3-jquery-validation-disable-unobtrusive-onkeyup

http://stackoverflow.com/questions/5487139/how-can-i-customize-the-unobtrusive-validation-in-asp-net-mvc-3-to-match-my-styl

Support creating extension methods with the @helper razor syntax, inside the APP_CODE folder.

This could be very useful, when creating html helpers, like the following code:

@helper ExtensionMethod(this HtmlHelper html, string data, string action)
{
<text>
<div>@data</div>
should I want to use Html here it is fine:
@html.ActionLink("Link text", action)
should I want to use Url here...
@{var url = new UrlHelper(html.ViewContext.RequestContext)}
@url.Action(action)
</text>
}

And be called inside any other view like this:

@Html.ExtensionMethod("Some text", "MyAction")

That'd be awesome! An easy way to make Html helpers!!!

I need preview for my html markup

Refactor the existing controller base class or implement an alternative implementation of the controller base class that does not depend on the httpcontext.. like the web api controller .

Support Display(Prompt="...") data annotation in order to render HTML5 placeholder tag with this value

The problem with the development with MVC is that we are used to ASP.net design view and drag and drop. If this is there is MVC it would be very easy.

Please fix this one: http://support.microsoft.com/kb/2816241

I don't know, why you restrict all EF 6 alpha/beta testers/users - I think the public part of the EF API the scaffolding use is already unchanged.

pick one and put it in the default templates

Open source the project templates or move them to nuget packages, but let the community fork them or extend them or make it easier to get into the new project dialog... its holding us back.

See for example this post by Hanselman http://www.hanselman.com/blog/ABackToBasicsCaseStudyImplementingHTTPFileUploadWithASPNETMVCIncludingTestsAndMocks.aspx that shows how troublesome the HttpContext is for testing.

The problem is that you have to stub several layers even if you only want to set a fake value for User for example. It would be great of this could be simplified so that it was possible to Mock/Fake only the properties/objects we need for that test.

I have to provide membership in an MVC web app to a Microsoft Dynamics CRM back end. CRM uses Guids as entity keys. The new simple provider forces the use of ints. Your old membership providers use Guids. Why not use generics so you can use any data type as key.

It should be possible to create bundles during runtime. It's not always possible to know beforehand what scripts/styles pages need. Or it's not practical to create many combinations of scripts/styles.

E.g

~/Views/Shared/_Layout.cshtml
@{
RegisterScript("~/jquery.js");
RegisterScript("~/bootstrap.js");
}

~/Areas/Admin/Views/Shared/_Layout.cshtml
@{
Layout = "~/Views/Shared/_Layout.cshtml";
RegisterScript("~/jquery-ui.js")
}

~/Areas/Admin/Views/Posts/Edit.cshtml
@{
Layout = "~/Areas/Admin/Views/Shared/_Layout.cshtml";
RegisterScript("~/post-edit.js");
RegisterScriptCode("function Foo(){...}");
}

We want better implementation of SimpleMembershipProvider that is not related to Sql server so we can use NoSql databases.
We also want implementation that is not that complex and that reference bunch of dlls (DotNetOAuth is very over complex library to do simple stuff)

It will be nice to have a fully supported and secure way to use forms and windows authentication in the same project. For example let's say that the project has three areas two of which can be managed using windows authentication but one of them can use forms connected to a custom database. In such way the app can support internal users and external users without having to deploy to separate apps.

I don't think I need to explain that one. But just in case we have DropDownListFor, why there's no RadioButtonListFor?