I\'m in the process of creating a new application and started out using EF6-rc1, Microsoft.AspNet.Identity.Core 1.0.0-rc1, Microsoft.AspNet.Identity.EntityFramework 1.0.0-rc
You can allow this by plugging in your own UserValidator on the UserManager, or just by turning it off on the default implementation:
UserManager.UserValidator = new UserValidator(UserManager) { AllowOnlyAlphanumericUserNames = false }