Hi,
just found a solution! It seems that there is a compatible driver afterall...
Go to this link (it's an official Samsung dutch site) and scroll down to where it says "Stuurprogramma" and download the Scan Driver which is for Mac OS 10.9 (61.44MB) http://www.samsung.com/nl/support/model/SCX-4623FN/SEE
If your Mac doesn't extract the zip automatically then extract it manually. Go into the extracted folder and launch "Installer OS X.app". Note that the Mac OS Gatekeeper might not let you open that file as it might treat it as malware etc (which is weird because the driver came from official Samsung site...). In that case just right-click on the file, then hold down ctrl and click on Open. That should do it. From this point on everything else is straightforward as in a casual installer. Note that you should quit any other open applications before installing scanner drivers!
Now the installer contains several different components (printer driver, scan driver, scan thru software and ica driver). I installed all of these components! Also note that the installer will ask you to restart your computer after it has installed just the first or second component, but don't restart it at this moment. Keep installing until you have installed everything you can (until there is no more installer icons in the dock) and after that you should restart your Mac.
When the Mac has restarted, connect your SCX-4200 to your Mac via usb and go into Applications folder and navigate to Samsung --> Scan & Fax Manager.app. Launch it and you should see your SCX-4200 listed in there which should let you use it as scanner...
Hope this helps.