Since the SS is available for everyone to read, this isn't spoiler territory.
Yes, there is a direct gateway between Arcana and Sharona. We also know that the physics of the two parent worlds are VERY different. I will remind us all that Shaylar can also communicate with cetaceans as a minor gift. Recall further that dragons responded to her and that she "heard" the dragon that carried her from Fallen Timbers. She didn't hear any meaning, but did experienced very unpleasant mental pressure from the dragon. We also know that Arcanan scout gryphons were being lost exploring into Traisum. Not through being killed but lost as in no longer being controlled by their crystals.
Now we learn in this short story that drakes can communicate with Sharonan orcas and dolphins. One assumes that whales can also communicate with the drakes too. If humans in Sharona can employ machines to excavate the rock blocking the gateway, it stands to reason that whales can move across. Not sure just useful that will by itself be since whales have been hunted to near extinction in Arcana. However, whales might be able to provide motive power to human submersible personnel carriers. Of course, the Arcanans might also use the portal to launch all sorts of nasty attacks on Sharona. I believe the gateway is a two edged blade in this regard.
What might be to Sharona's advantage with the undersea gateway is the discovery Gadriel made after the firearm demonstration in Arcana. Will the principle that Sharonans use in their science allow Shaylar and Jathmar is impact Arcana society more deeply after they discover the undersea gateway? One suspects this is likely. Especially since arcana can already cast WMDs at Sharonans in universes where magic works. If that principle is something like magic being influenced by the beliefs of the sentients residing in the universe, then Shaylar and Jathmar can destroy Arcanan society by persuading the mundanes there to adopt Sharonan technology that does not require magic. I can see that being especially effective and likely to succeed in Mythal. Once that belief takes hold somewhere, it weakens magic everywhere.
Both societies will have an element to assure mutual destruction absent some sort of peaceful resolution to the hostilities.
