As for "The three shall become one", the minute I read that I became convinced the characters had it wrong and this had to refer to Rand, Mat and Perrin and their mental link. Mat in turn is linked to the Finns, Perrin to the wolves and Rand to Moridin. In think at some point in the Last Battle, Rand will literally have to be at many places at once, and do many things at once. He won't, it will be the three ta'veren, in perfect coordination. The wolves and the Finns? We'll see.

As for the Finns/Ogier, our ideas are pretty close. My general idea is that people aren't meant to do things like linking by portal and visiting the "If Worlds", the other dimensions (like the ones in which Snakes, Foxes, Ogier live), or even to enter a dimension like Tel'aran'rhiod in the flesh, or to build transportation systems in the dimension between worlds, messing up time and space (like the Ways). BY the physical rules of Creation it's possible to do all these things, and apparently someone does at some point every turning of the wheel, but it comes at a price, and yes I think it's an allegory for hubristic science and a nod to what Jordan alluded may have marked the end of our own time (atomic war).

What I think is that by connecting the worlds and opening portals between the worlds, the race who did that in an earlier Age (and I think it is the Finns) have created a "cosmic accident" that has resulted in three main things: First, it has made the Finns abandon the Portal Stones and their other quantum physic experiments. The accident has made the two Finn worlds and the human world collide, and the place where they fused (become fold together) has been circumscribed by making the Tower of Ghenjei. The second effect it caused is to make scattered pieces of another world, the Ogier's, merge randomly with the world of humans. I think stedding are just that: they aren't made, they can't be made. Stedding, and their characteristics, are simply the rules of reality as they are in the Ogier homeworld (no channeller or channelling access, Tree Singing, etc.), and pieces of this world have been translated in another world, with other rules. The most dire effect the accident caused is that it globally weakened the pattern, just enough that Shai'tan's prison could now be sensed. At the end of their own Age, the Aes Sedai fell to hubris either. They started playing with the numbers of chaos they barely undestood, tried to puzzle out how the science of the PS and eventually, Beidomon and Mierin and the others tried to open a portal to this second "True Source" (I think they believed it may be the real true source outside creation, the raw power before it gets divided into saidar and saidin to weave the pattern) and instead of linking this source to the world via a portal, this resulted into the Bore and the Dark One starting to touch Creation. They never really understood what had happened and why, they spent much of the Collapse and the whole WOS trying to understand the nature of the Bore, and how to close it. They even kept making portal to vacuoles, and in the Breaking years they made the Ways.

I think that to repair the Pattern, the portals between worlds will need to be closed down for good (until the next turning). They are part of the "rubble" Rand needs to clear out before the Bore can be repaired, instead of patched the way LTT intended or shielded the way Latra intended.

So, I suspect it's important that the Ogier "translate" at the right time, and so be convinced to stay for the LB (the general idea may be that for all this to work, it may have to be done in coordination, or else all it will achieve is to make the whole pattern unravel), and I also suspect that's the real importance of Mat returning to the Finns, and accepting and understanding why it's important that they keep seeing the world of humans through one of his eyes. Whatever the Finns have to do, they will do through Mat. I also think it's important to close down all the Waygates, as I suspect Shai'tan will be able to break the barriers between them and his prison sooner than he'll be able to get out of the Bore, in effect during the LB the Bore wouldn't be in one place and a global weakness at the same time anymore, it would become "in many places and a global weakness at the same time" - "the Blight", the DO's direct touch, would spread around the Waygates just guarded instead of "killed" by removing the Avendesora leaf... and most Waygates are near cities and stedding. The worst of that Jordan averted by having Rand close the Ways on other motives (including the most dangerous ones that would kill off much of the main cast like Elayne and Mat in Caemlyn, Egwene in Tar Valon, Tuon in Ebou Dar and end the story...), but the task isn't finished yet.