The plugin system seems to be working well. It is now integrated with the GUI and configuration file. The naming scheme in the configuration file has changed slightly, but old values will be recognized and replaced. So if you had different settings for every game in your game library, they should all still work.
In addition, I added a 4x nearest neighbor scaler. It works fine except for some minor cursor issues which should be fixed when the cursor api gets changed. This means HQ4x and AdvMame4x will soon be available with very little added code.
Now I am in the process of removing quick hacks I made earlier. Then much of the scalers need to be changed to fully implement more pixel formats.