In Part 5 we see Dalinar managing to gather enough power (presumably through his bond with the Stormfather a.k.a. Honor's Cognitive Shadow?) to force Honor's Perpendicularity to manifest in Thaylen City. If he can gather that much power by saying an Ideal and defying Odium, then would it be possible for him to, however it may work, gather Honor's different splinters and actually take them all up together, thereby mending Honor's Splintering and becoming Honor? We know, after all, that Splintering can be undone.
This may even be what Honor means with "Unite them", though I would argue that is open for debate, as we also know that Honor could barely/not at all see into the future, though of course Cultivation might have seen it happening. We did get a RAFO on that, after all.