I spoke to Centurion customer services in the UK about this. They are noteably clueless regarding even existing benefits, and the rep had no idea, but said she would go away and speak to marketing.
She called me back and said words to the effect "we cannot confirm anything at this time, but are always looking to enhance our benefits. If the situation changes we will be notifying you", which was very clearly signalling without confirming that this rumour has substance. My only concern is that this will be targeted to certain high volume (or non One world) travellers, but I think its unlikely Amex could justify a targeted benefit (as opposed to one off give-aways) - it would be out of step with how the programme has always been.
I now believe this is real, and we should watch this space. As I understand it top tier OW would allow access to the BA First lounge at T5 at most other Gold Card benefits - a very considerable benefit, argueably (depending on your particular flying patterns etc) the most valuable benefit of the card