Mantis#1591. Thank you graciously, Sempuki for a patch that:

Currently module loading is done ad-hoc. I propose creating a simple 
loader class that leverages Mono.Addins (and perhaps the new .NET 
addins when they become available in mono). Attached is a basic 
patch for review that compiles into HEAD, but doesn't yet replace 
any existing ad-hoc loaders.

OpenSim/Framework/PluginLoader.cs

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSim Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+using System;
+using System.IO;
+using System.Collections.Generic;
+using System.Reflection;
+using log4net;
+using Mono.Addins;
+
+namespace OpenSim.Framework
+{
+    public class PluginLoader <T> : IDisposable where T : IPlugin
+    {
+        private static readonly ILog log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
+        private List<T> loaded = new List<T>();
+
+        public PluginLoader (string dir)
+        {            
+            AddPluginDir (dir);
+        }
+
+        public void AddPluginDir (string dir)
+        {
+            suppress_console_output_ (true);
+            AddinManager.Initialize (dir);
+            suppress_console_output_ (false);
+        }
+
+        public delegate void Initialiser (IPlugin p);
+        private void default_initialiser_ (IPlugin p) { p.Initialise(); }
+
+        public void Load (string extpoint)
+        {
+            Load (extpoint, default_initialiser_);
+        }
+
+        public void Load (string extpoint, Initialiser initialize)
+        {
+            AddinManager.Registry.Update (null);
+
+            ExtensionNodeList ns = AddinManager.GetExtensionNodes(extpoint);
+            foreach (TypeExtensionNode n in ns)
+            {
+                T p = (T) n.CreateInstance();
+                initialize (p);
+                Plugins.Add (p);
+
+                log.Info("[PLUGINS]: Loading plugin " + n.Path + "/" + p.Name);
+            }
+        }
+
+        public List<T> Plugins
+        {
+            get { return loaded; } 
+        }
+
+        public void Dispose ()
+        {
+            foreach (T p in Plugins)
+                p.Dispose ();
+        }
+
+        public void ClearCache()
+        {
+            // The Mono addin manager (in Mono.Addins.dll version 0.2.0.0) occasionally seems to corrupt its addin cache
+            // Hence, as a temporary solution we'll remove it before each startup
+            if (Directory.Exists("addin-db-000"))
+                Directory.Delete("addin-db-000", true);
+
+            if (Directory.Exists("addin-db-001"))
+                Directory.Delete("addin-db-001", true);
+        }
+
+        private static TextWriter prev_console_;
+        public void suppress_console_output_ (bool save)
+        {
+            if (save)
+            {
+                prev_console_ = System.Console.Out;
+                System.Console.SetOut(new StreamWriter(Stream.Null));
+            }
+            else
+            {
+                if (prev_console_ != null) 
+                    System.Console.SetOut(prev_console_);
+            }
+        }
+
+    }
+}