Think this is a good way to manage events, since many will be targeted between specific nodes. It is expected for developers to cast as needed.

api/src/main/java/net/md_5/bungee/api/PendingConnection.java

@@ -0,0 +1,8 @@
+package net.md_5.bungee.api;
+
+/**
+ * Represents a user attempting to log into the proxy.
+ */
+public interface PendingConnection extends Connection
+{
+}

api/src/main/java/net/md_5/bungee/api/event/ChatEvent.java

@@ -1,28 +1,33 @@
 package net.md_5.bungee.api.event;
 
 import lombok.Data;
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
 import net.md_5.bungee.api.Connection;
-import net.md_5.bungee.api.ProxiedPlayer;
 import net.md_5.bungee.api.plugin.Cancellable;
 
+/**
+ * Event called when a player sends a message to a server, or a server sends a
+ * message to a player.
+ */
 @Data
-public class ChatEvent implements Cancellable
+@ToString(callSuper = true)
+@EqualsAndHashCode(callSuper = true)
+public class ChatEvent extends TargetedEvent implements Cancellable
 {
 
     /**
      * Cancelled state.
      */
     private boolean cancelled;
-    /**
-     * Where this message is being sent to.
-     */
-    private final Connection destination;
-    /**
-     * User involved with sending or receiving this message.
-     */
-    private final ProxiedPlayer player;
     /**
      * Text contained in this chat.
      */
     private String message;
+
+    public ChatEvent(Connection sender, Connection receiver, String message)
+    {
+        super(sender, receiver);
+        this.message = message;
+    }
 }

api/src/main/java/net/md_5/bungee/api/event/LoginEvent.java

@@ -1,7 +1,7 @@
 package net.md_5.bungee.api.event;
 
-import java.net.InetAddress;
 import lombok.Data;
+import net.md_5.bungee.api.PendingConnection;
 import net.md_5.bungee.api.plugin.Cancellable;
 
 /**
@@ -20,15 +20,7 @@ public class LoginEvent implements Cancellable
      */
     private String cancelReason;
     /**
-     * Username which the player wishes to use.
+     * Connection attempting to login.
      */
-    private final String username;
-    /**
-     * IP address of the remote connection.
-     */
-    private final InetAddress address;
-    /**
-     * Hostname which the user tried to connect to.
-     */
-    private final String hostname;
+    private final PendingConnection connection;
 }

api/src/main/java/net/md_5/bungee/api/event/PluginMessageEvent.java

@@ -1,29 +1,24 @@
 package net.md_5.bungee.api.event;
 
 import lombok.Data;
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
 import net.md_5.bungee.api.Connection;
-import net.md_5.bungee.api.ProxiedPlayer;
 import net.md_5.bungee.api.plugin.Cancellable;
 
 /**
  * Event called when a plugin message is sent to the client or server.
  */
 @Data
-public class PluginMessageEvent implements Cancellable
+@ToString(callSuper = true)
+@EqualsAndHashCode(callSuper = true)
+public class PluginMessageEvent extends TargetedEvent implements Cancellable
 {
 
     /**
      * Cancelled state.
      */
     private boolean cancelled;
-    /**
-     * Dispatcher of this message.
-     */
-    private final Connection sender;
-    /**
-     * Player involved with sending or receiving this message.
-     */
-    private final ProxiedPlayer player;
     /**
      * Tag specified for this plugin message.
      */
@@ -32,4 +27,11 @@ public class PluginMessageEvent implements Cancellable
      * Data contained in this plugin message.
      */
     private byte[] data;
+
+    public PluginMessageEvent(Connection sender, Connection receiver, String tag, byte[] data)
+    {
+        super(sender, receiver);
+        this.tag = tag;
+        this.data = data;
+    }
 }

api/src/main/java/net/md_5/bungee/api/event/TargetedEvent.java

@@ -0,0 +1,20 @@
+package net.md_5.bungee.api.event;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import net.md_5.bungee.api.Connection;
+
+/**
+ * An event which occurs in the communication between two nodes. It is not
+ * recommended to call {@link #setSender(net.md_5.bungee.api.Connection)} or
+ * {@link #setReceiver(net.md_5.bungee.api.Connection)} and the results of doing
+ * so are undefined.
+ */
+@Data
+@AllArgsConstructor
+public abstract class TargetedEvent
+{
+
+    private Connection sender;
+    private Connection receiver;
+}