The arrival of the Grey Council via lightning strikes was a fortuitous arrival, (i.e. Fate point expenditure on behalf of the travelers) themed by the fact that one of the travelers was friggin Odin.
The first portal that was opened to let the Bird-Men charge in (Genku, Ginku... i forget their name), was simply a pretty large portal into the nevernever, with the Birdies waiting on the other side.
No special mechanics needed. Can be done with Ritual(Worldwalking), Thaumaturgy or Worldwalking. Leaving aside the natural crossing abilities all Supernaturals seem to have. (Think Thomas in Grave Peril or White Night)
The second Portal was a Handwave. I mean come on... created by a friggn Odin, it's use "negotiated" by the most powerful vassal of the Winter Court.
It was a narrative shortcut. Otherwise Jim would probably just have said that they chose a different, longer, less perilous route through the nevernever to get back to Chicago. It was important that they got back, not how or how fast.
I would not let players create such portals to use for dramatically or tactically important travel. They'd be narrative only, and if you only use them as a narrative shortcut, then they really don't need mechanics.
Edit: i just realized that the issue posted by the OP is not IF they should be used by players, but how to stat them. Sorry for being less than helpful *g*
