We have got exactly one new piece of information about Multiverse #3 so far. The title is "The Road to Hell" so what could that mean? I see a few possibilities.
1) Everyone is calling the universe where they met Hell's Gate. One glaringly obvious possible plot moving forward is that the Sharonans are going to try and advance from Fort Shaby back to Hell's Gate. The railroad that they laid as they did so could be reasonably called "The Road to Hell." The title might hint that the effort to build that road is the military center of the story.
2) The title could also be a reference to the saying "The road to hell is paved with good intentions." I personally think that while he is wrong in some many ways it would take me an essay to describe them all 2000 Harshu does seem to have tried to do what was best regardless of the personal cost. So his intentions are good. If you take a sufficiently relative definition of "good intentions" even mul Gurthak could be said to have "good intentions". After all he is trying to make the world into what he believes it ought to be. I find it easy to imagine that a key part of this book could be the process by which, in trying to do what is right the Sharonan leadership manages to make things even worse.
3) The title could just be a metaphor for the direction this series is going and how bad things are going to get.
And yes I know trying to guess this based on the title of a Weber book is foolish but we don't have anything else to go on yet so I thought it would be fun to make the effort.
Nicholas