That would ultimately depend on how badly in deficit the scheme itself was. So in theory, if the scheme was only 70% funded, pensioners could face a 30% haircut on their pensions.
That said, there is talk that there could be a "guaranteed minimum pension" that would be protected. So if the minimum amount was, say, €12,000, that level would be protected and any pension over and above that could be subject to a haircut.
But as you say, all of this is just speculation as nothing has been announced.