I think what it meant when it said Ascend with a capital A was that Odium was trying to get Dalinat to ascend to the fused, as he later implies in RoW is possible, but dalinar stopped that when he started yelling and then swore the ideal.
For Unity, I think it meant that, as lift is partially in the cognitive realm, Dalinar and the Stormfather and partialling in all three.
Also, another random theory, there are three main shallan personas. Is each one associated with a realm?
for cognitive seems like veil, and in the physical realm she is shallan, so does that mean that radiant is associated with the spiritual realm? if so could she do things differently that a regualr lightweaver, as we see dalinar doing things differently than a regular bondsmith, and with my theory he is partially in the spiritual realm.