Living Shardplate and the fifth oath.

[NameIess]

Here it is, my (probably) last theory before RoW comes out. A lot of speculation has gone into what benefits the fifth ideal will give Radiants, as it has been confirmed not to grant the obvious answer, perfect stormlight efficiency: 

Quote

Zykai (paraphrased)

Squires and people wielding Honorblades use more Stormlight than a regular Radiant. Who uses more?

Brandon Sanderson (paraphrased)

The further you progress, the more efficient you become at consuming Stormlight. They're never as efficient as the Voidbringers, since humans leak too much.

Stuttgart signing (May 17, 2019)

Since the lesser spren theory for Shardplate was pretty much confirmed in the Syl interlude, here is my theory about how that will work exactly. Whenever Kaladin considers the fourth ideal, or is fulfilling his ideals particularly well, he gathers windspren. Shallan gathers creationspren, and Dalinar gathers gloryspren (Although he doesn't get plate). My theory is this: when a Radiant swears the fourth ideal, they reach the bare minimum connection to their spren, which the gives them just enough, or even just below enough, connection to their secondary spren to summon Shardplate. In order to get the correct level of connection, they need to be embodying their ideals particularly strongly. Upon swearing the fifth ideal, the Radiant will gain a connection to their spren that is strong enough to allow them to summon Plate at any time.

[Kuram]

I think the fifth will just allow for exceptionally powerful surgebinding.  Not very imaginative, I know.

[Truthwatcher Artifabrian]

I feel like a lot of the surges are not currently being used to their full potential. Adhesion is the surge of pressure and vacuum, and all we’ve seen windrunners use it for is a full lashing. At one point Kaladin did use it more, when he redirected the storm around himself.

 What if the fifth ideal allows radiants to always use this full potential, instead of just the very specific lashings and uses of surges. And before the fifth ideal, they can only use it when they are REALLY embodying their oaths.

[Halyo_Alex]

My personal, very crackpot hypotheses with minimal evidence for the 5th oath's effect are as follows:

1. The bond deepens sufficiently to make the spren and Radiant indistinguishable spiritually, and so they become a single entity with the most efficiency in holding Stormlight that the Radiant can have. They have complete understanding of their Surge pair, and so can naturally use it in ways that others cannot without proper instruction.

2. (and this is the less likely one) The radiant gains the ability to command their order's Essence (air, smoke, fire, crystal, etc) to move as they desire, consuming Stormlight in the process. The evidence for this is pretty flimsy; the beta Radiants were once all capable of Soulcasting, but only to make stuff into their own order's essence. This would basically be that concept reimagined now that the Surge of Transformation exists. (And yes, this means 5th ideal Stonewards are Earthbenders, pretty much).

Of course, the big evidence against either of these is our favorite herald, Nale. He's a 5th oath skybreaker... But afaik he hasn't needed to smokebend (jeez that sounds weird... need a better term), and maybe the benefits of the fusion are less pronounced for him because he's a Herald and is therefore a cognitive shadow, maybe his body doesn't change appearance like others might, though... We don't see his spren on screen do we? Hm.