I have lurked for years and do not normally post. Dalinar is a Stoneward Bondsmith and not a Skybreaker. His oath is to unite and not divide. Therefore, I believe that he will see that punishing Adolin harshly will not only cause his family ruin, but cause a fracture among the Radiants. All Radiants or Surgebinders known to him at this time either care for Adolin greatly or despise Sadeas, so I believe that it is safe to hypothesize that this will be a major internal conflict for Dalinar. While Dalinar will be pushed by the High Princes to seek justice for Sadeas’s murder, Dalinar will choose to unite the Knights Radiant instead. Everything that Dalinar has done to this point was to unite Alethkar, but the scope of his vision has changed by the end of WoR. All of Roshar is in danger, plus eventually Dalinar must find out why Gavilar was assassinated in the first place.
I also do not believe that Adolin is the traitor to which the quote is referencing. One we have no clue who the others are in this case. As someone stated earlier it could very well be one of the Unmade. I believe it could also be referencing one of the orders in its entirety. But my hunch is that it is one of the orders of Voidbringing. I believe that the Stormfather said Odium might be able to be defeated if he were to promote a Champion. I think that the traitor will be Eshonai. No proof just fancy.