WinUAEX v17 is fully open source. Feel free to download and post updates.
The author, X-port, retired in 2007.
WinUAEX v17 is based on a VERY old version of WinUAE but moving to the latest core (just introducing the latest files) is not possible without work. I know, I tried.
Back-porting fixes to WinUAEX from the latest core is extremely difficult as too many things have changed. You need to start at the version WinUAEX was based on and move forward.
Also the newer versions of WinUAE require more CPU power than earlier versions and v17 is only borderline full speed as it is.