There have been rumours ever since Chrysler/Valiant left the competition and Nissan Skylines were ruled out.
I honestly don't think we are likely to see a third manufacturer enter the competition any time soon, for many reasons but mostly the fact that Holden and Ford make too damn much money out of it to let anyone else in.
Unfortunately, the Bathurst Annual has become far too commercialised and is no longer accessible to the 'everyday rev-head', there are a number of lower tear competitions and club runs that utilise the Mount Panorama circuit but it's no longer like the era that Brocky started in - that's for sure.