I don't think we'll see it yet in Peace Talks, or even Battle Ground... But I observe the Jim has laid the groundwork for a really potent power-up for Harry.
We know that point-to-point Gateways are possible, apparently by creating back-to-back openings to the Nevernever, such that you can step into one gate and out of the other, in the same step.
We know that you can cast across a Nevernever-gate. Cowl attacked Harry that way (in the Raith Deeps), etc.
In principle, then...
Harry could stand on Demonreach, with full Warden power and all those ley-lines, and open a gateway to wherever he needs to be really REALLY powerful.
(edit: I guess this is a WAG, more than an on-topic post for the thread... apologies; "wannasee tax" -- Gotta +1 looking forward with both dread and amusement to the scene where Molly tells her 'rents "oh yeah... now I'm a faerie, and immortal, and...")