Why Not?
Given the future size, shape and employment of the UK armed forces, it would make sense to combine all officer training in one purple establishment. The current story may just be an ill informed rumour, but the fact is - it would make sense. Go back 20 years and I doubt anyone could have predicted the JSCSC at Shrivenham. However, it works and makes sense. Nevertheless, the would be no point of the RN and RAF combining, with the brown jobs remaining at Sandhurst - close all three or none at all.
IMHO sooner or later some form of combined inital officer training will be introduced, it's only a matter of when, not if. Forget traditions, as usual it will all come down to simple economics.