Maybe, Zeus himself is also planning something. But all of this is just conjecture in Hades part and he did not say this to Poseidon.
As for the matter of the Underworld, Hades knows the general direction of the future.
So, when Hypnos a Charon send him a proposal to expand the channel of the dead he rejected it
The channel should be created so that when congestion of the souls entering the Underworld happens, a new channel of queuing up for the souls would be opened.
That was the purpose of opening a new channel.
But something has changed.
And Hades had a bad feeling that this must have been tied with the Child of the End.
Only he…..someone that is the integral part of this story could have such an effect that changes the reality and projected future.
so, for now he simply close all the doors and portals and any other secret hidden dimension to enter the Underworld.
