HitObject -> HitBase. Also add BaseHits for each game mode.

osu.Game/Beatmaps/Beatmap.cs

@@ -10,7 +10,7 @@ namespace osu.Game.Beatmaps
 {
     public class Beatmap
     {
-        public List<HitObject> HitObjects;
+        public List<BaseHit> HitObjects;
 
         public List<ControlPoint> ControlPoints;
 

osu.Game/Beatmaps/Objects/BaseHit.cs

@@ -8,7 +8,7 @@ namespace osu.Game.Beatmaps.Objects
     /// <summary>
     /// A hitobject describes a point in a beatmap 
     /// </summary>
-    public class HitObject
+    public abstract class BaseHit
     {
         public double StartTime;
         public double? EndTime;

osu.Game/Beatmaps/Objects/Catch/CatchBaseHit.cs

@@ -0,0 +1,11 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+
+namespace osu.Game.Beatmaps.Objects.Catch
+{
+    class CatchBaseHit : BaseHit
+    {
+        public float Position;
+    }
+}

osu.Game/Beatmaps/Objects/Mania/ManiaBaseHit.cs

@@ -0,0 +1,11 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+
+namespace osu.Game.Beatmaps.Objects.Mania
+{
+    class ManiaBaseHit : BaseHit
+    {
+        public int Column;
+    }
+}

osu.Game/Beatmaps/Objects/Osu/OsuBaseHit.cs

@@ -0,0 +1,12 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using OpenTK;
+
+namespace osu.Game.Beatmaps.Objects
+{
+    public abstract class OsuHit : BaseHit
+    {
+        public Vector2 Position;
+    }
+}

osu.Game/Beatmaps/Objects/Taiko/TaikoBaseHit.cs

@@ -0,0 +1,19 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+
+namespace osu.Game.Beatmaps.Objects.Taiko
+{
+    class TaikoBaseHit : BaseHit
+    {
+        public bool Big;
+
+        public TaikoColour Type;
+    }
+
+    public enum TaikoColour
+    {
+        Red,
+        Blue
+    }
+}

osu.Game/GameModes/Play/PlayTest.cs

@@ -1,7 +1,10 @@
 //Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
 //Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System.Collections.Generic;
 using osu.Framework.GameModes;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Objects;
 
 namespace osu.Game.GameModes.Play
 {
@@ -10,6 +13,14 @@ namespace osu.Game.GameModes.Play
         public override void Load()
         {
             base.Load();
+
+            Beatmap beatmap = new Beatmap();
+
+            beatmap.HitObjects = new List<Beatmaps.Objects.BaseHit>()
+            {
+                new HitObject() {  },
+            };
+
         }
     }
 }

osu.Game/osu.Game.csproj

@@ -48,7 +48,11 @@
     <Compile Include="Beatmaps\Beatmap.cs" />
     <Compile Include="Beatmaps\BeatmapSet.cs" />
     <Compile Include="Beatmaps\Metadata.cs" />
-    <Compile Include="Beatmaps\Objects\HitObject.cs" />
+    <Compile Include="Beatmaps\Objects\BaseHit.cs" />
+    <Compile Include="Beatmaps\Objects\Catch\CatchBaseHit.cs" />
+    <Compile Include="Beatmaps\Objects\Mania\ManiaBaseHit.cs" />
+    <Compile Include="Beatmaps\Objects\Osu\OsuBaseHit.cs" />
+    <Compile Include="Beatmaps\Objects\Taiko\TaikoBaseHit.cs" />
     <Compile Include="Beatmaps\Samples\HitSampleInfo.cs" />
     <Compile Include="Beatmaps\Samples\SampleBank.cs" />
     <Compile Include="Beatmaps\Samples\SampleInfo.cs" />