Eliminate the NodeHostingModel enum because it isn't extensible. Instead, use extension methods on NodeServicesOptions to configure a NodeInstanceFactory.

src/Microsoft.AspNetCore.NodeServices/HostingModels/NodeServicesOptionsExtensions.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace Microsoft.AspNetCore.NodeServices.HostingModels
+{
+    /// <summary>
+    /// Extension methods that help with populating a <see cref="NodeServicesOptions"/> object.
+    /// </summary>
+    public static class NodeServicesOptionsExtensions
+    {
+        /// <summary>
+        /// Configures the <see cref="INodeServices"/> service so that it will use out-of-process
+        /// Node.js instances and perform RPC calls over HTTP.
+        /// </summary>
+        public static void UseHttpHosting(this NodeServicesOptions options)
+        {
+            options.NodeInstanceFactory = () => new HttpNodeInstance(options);
+        }
+
+        /// <summary>
+        /// Configures the <see cref="INodeServices"/> service so that it will use out-of-process
+        /// Node.js instances and perform RPC calls over binary sockets (on Windows, this is
+        /// implemented as named pipes; on other platforms it uses domain sockets).
+        /// </summary>
+        public static void UseSocketHosting(this NodeServicesOptions options)
+        {
+            var pipeName = "pni-" + Guid.NewGuid().ToString("D"); // Arbitrary non-clashing string
+            options.NodeInstanceFactory = () => new SocketNodeInstance(options, pipeName);
+        }
+    }
+}