With the reveal of the final Shard intent being Reason, race to make tables and groupings of Shards has already begun, but ever since I read Mistborn Era I I always theorized that different Shard Intents could have opposites, pushes and pulls, like Preservation and Ruin do, and I'm surprised just how little I've seen this idea on the forums. It could be that I'm just not paying enough attention lol, but regardless, here is my list and reasoning for each Shard pairing, and I'm interested in what you all think.
Preservation - Ruin
This one is pretty obvious, and is made clear during Era I, them being the embodiments of stasis and entropy, permanence and change. It's also displayed in Era II, in Harmony's inability to act because of the polarity of the Intents. I find it notable that Retribution has no such limitation, so it's not a side effect of being a double Shard. You could argue that Ruin and Preservation are a special case, but again, I feel that it's simpler than that.
Endowment - Cultivation
This one makes a lot of sense to me, because it's the relationship between having something be given to you, vs having it be built up, cultivated, over time. One has the sense of something more immediate, or involving an exchange, and the other is a slow build, involving care and toil. Not to say that Endowment doesn't care, and the magic systems and actual personalities of the Vessels aren't really as significant in this discussion as simply the Intents themselves, as we understand them.
Honor - Mercy
This one is interesting, and in my mind has only become strengthened by the new perspective on Honor offered to us by the events of Wind and Truth. That being the idea that Honor is not morality, and in some cases is even a lack of such, as it only really cares about keeping one's word, and holding to Oaths, even if there are terrible things being sworn. Mercy is the willingness to break oaths, forgive debts, and do what is right despite the fact that punishment might be "justified". Think of honor killings, or the old samurai tradition of seppuku, wherein they kill themselves to avoid shame falling upon their family or to atone for grievous crimes. Mercy can also be violent, and the term "mercy kill" is also one that exists, but it is quite often pitted against the idea of honor in history and pop culture.
Autonomy - Dominion
Now, we don't know much about Dominion from Elantris, other than the effects that her presence had on the landscape of Sel. However, looking simply at the word we've been given to describe the Shard's Intent, it makes the most sense to associate it with domination, control, and hierarchy. This doesn't necessarily mean subjugation or oppression, as we've seen pretty much every Shard has both a good and bad side/interpretation, but you could see how Autonomy would play against Dominion, being the soul of freedom and self-determination. Again, Bavadin herself is rather domineering, but I bring up again that the Vessel's personality isn't relevant.
Invention - Virtuosity
These two Shards stand out a little bit among the others, but when you get into it a little bit, it makes sense that they would be opposites, because they are essentially the difference between form and function. Invention --as it has been interpreted by the fandom thus far-- is often viewed as a creature of industry, mechanics, Grand Apparatuses, if you will (Apparati?). Necessity is the mother of invention, as they say, and thus Invention seeks to remedy problems. Hoid has, many times, asserted that art is pointless, and loses meaning when it is given a function. Whether or not you agree with this point of view, it displays a clear opposition between art (Virtuosity) and Invention.
Devotion - Whimsy
This is another pairing which could be relatively obvious. Devotion is commitment, consistency, and even divine love and compassion as we've been told in WaT. Whimsy is by definition flippant, capricious, and relatively uncaring, jumping from idea to idea, whim to whim, without consistency or commitment to anything.
Odium - Reason
This was a pairing that I was so satisfied to be able to make a connection on. For so long I had been waiting to find a good foil for Odium, and with the introduction of Reason, I believe it can be the only answer. We've gotten really up close and personal with Odium in the last two Stormlight books, and its Intent has been introduced as a thing which feeds on emotion, sacrificing logic for passion. We see this in Taravangian and his condition before he ascended, where his compassion and ability to feel emotions could not exist at the same time as his practicality and stark decision making. It's the head vs the heart. We know very little about Reason, but I think that the word that was eventually chosen is the perfect opposite to Odium.
Valor - Ambition
Now... this pairing is the only one I'm still working out, and I'm not sure I have a full explanation for how they could be opposites. We know so little about either of them, and they were sort of the leftovers when I was making a chart, but in talking with others we've theorized that it could potentially be something along the lines of Valor being self-sacrifice and bravery in defending others, and Ambition is looking out for one's own self or kin? It's difficult because these two words could in some cases be interpreted as synonyms, and have the same sort of zeal and innate sense of action in them, but I think there could be an argument made.
So that's all that I have, and I'm interested to hear what you all think!