Closed Feature: HttpHeaders collections should benefit from IEnumerable covariance [1127]

Every HttpHeaders collections access from HttpRequestHeaders, HttpResponseHeaders, HttpContentHeaders that takes one of these type parameter:
MediaTypeWithQualityHeaderValue , NameValueWithParametersHeaderValue, TransferCodingWithQualityHeaderValue
should use their less specialized type parameter (without With_X_ in the type name) to benefit from IEnumerable<T> covariance. These collections construction or update should integrate default settings or type casting for Quality or Parameter but their concrete type should stay the more specialized one.
Comments: Hi SebM, I logged this bug in the internal Microsoft bug database so that the team that owns this code can look into addressing this. If you like, you can also open an additional bug via Microsoft Connect (https://connect.microsoft.com/VisualStudio). Thanks, Eilon