I have spoken to my dealer & they have confirmed they have heard rumours, but they are normally the last too know!
I cannot imagine "Car magazine" publishing information & this not becoming reality. Also the Mk4 GTI started life with the 115BHP & this increased to other options for the 150BHP & 180BHP, so don't be surprised if the 237BHP becomes available, perhaps for the Anniversary.
I am personally not interested in increasing the BHP of the standard GTI with chips etc. However, if VW did introduce a more powerful GTI as standard, I would be very interested. Albeit that I only took delivery of my GTI on Wednesday!