I'll cut to the chase: Dalinar is Honor. Rather, Dalinar is the future vessel of Honor. Hear me out...
"Unite them"
This has been Dalinar's driving motto from the beginning. "Unite" who? The highprinces? The Radiants? The people of Roshar? I don't have a copy of the books in front of me, but here is my logic:
We know that all spren are splinters of investiture that gained sentience. Some other spren have gained sapience as well. Radiant spren, for example.
We know that all the 'original' Honorspren, except for Syl, where killed in the recreance.
We know that Odium "killed" Honors vessel, Tanavast, splintering the shard.
Tanavast knew he was going to die and prepared.
He 'super-invested' the stormfather.
He gave the stormfather the visions and the ability to manipulate them.
He probably did other things too that we don't know about yet or that I am forgetting.
The driving impetus was for the stormfather to find someone worthy to give the visions to and impart the drive to "unite them".
Dalinar exhibits power and abilities that the stormfather doesn't know of.
** Dalinar somehow has the ability to accept the oaths of rising Radiants. **
Unless we are missing something about bondsmith abilities, this shouldn't be possible.
Only the Radiant spren or their 'parent' can accept the 'Words'.
Dalinar is still a Radiant, albeit of the most powerful order.
Thus, in terms of the overarching hierarchy, Dalinar is still at the same level as any other radiant in terms of advancing in ideals.
Yet he was still able to accept Kaladin's oath.
It is said many times in all the books that "Honor live on in the hearts of men".
Which explains why there are still Honorspren.
Since Honor lives in the hearts of men, and humans must have been heavily invested before Tanavasts death, then the 'new' Honorspren are formed formed through the Honor of humans and their investiture.
My theory, then, is that while Odium may have killed Tanavast, Tanavast splintered the shard of Honor, heavily investing the stormfather and also investing humans. As such, the "Unite them" impetus is referring to Honor's splinters. As in, unite the splinters of Honor back into the shard and take it up as the vessel.
Dalinar is on the journey to become the vessel of Honor.
Other predictions:
Kaladin is a dawnshard. He became such through Syl, who was given the shard to pass on to a worthy individual. Syl, the Ancient Daughter and only surviving Honorspren from when Honor was still 'alive'. No other theory *really* fits with Kaladin's abilities throughout the books and meshes with other well researched theories.
Adolin will 'awaken' Maya and they will bond... thus setting the precedent for waking all the deadeyes, if given the chance.
That is all, for now