I do not believe that we will see four new tunnels built in the lifetime of anyone currently living. At best two will be built with provisions for the other two to be built at a future date. The money simply is not there for four new tunnels given all other priorities.
I am OK with the fact that they planned all the bells and whistles (double stack under wire) in all of them. The savings to be had from making two of the tunnels not-double stack compatible are vanishingly small as the costs do NOT scale with the tunnel diameter. The only thing that scales with diameter is the removal of the spoils and the energy required to bore the tunnels. A bigger tunnel boring machine rarely requires more people to run it and all the wires, tracks, signals and so on are practically the same regardless of the size of the bore.
And to answer an earlier question. I do not believe that the national fire codes specify the exact distance between exits and such for rail tunnels, but the principles embedded in the code effectively require those exits. Note that a freight tunnel does not require as frequent exits and the same level of egress capability (the new Virginia Avenue Tunnel on CSX comes to mind). I cannot recall the last time I heard of a single track passenger tunnel being built anywhere in the developed world. Egress capability always makes two tunnels necessary even in places which are less concerned about passenger safety. Some places even require three bores with the third one used for ventilation and egress (the Channel Tunnel comes to mind).