I agree with you on what the 4th ideal is likely to be about. How ever i disagree that were going to see Kaladin swear it in the 4th book without massive external help getting over his hangups. The sort of help that might've been provided by a caring and understanding partner but alas we are in the broodiest time-line.
As I said earlier I think this particular dysfunction of Kals will actually make him a worse radiant, but a better herald. Especially if you consider that by not giving in to the torture of the voidbringers* he will effectively be protecting everyone, humans and parshmen alike. And by suffering eternally no less! A perfect situation for Kaladin powered-by-my-own-suffering Stormblessed.
Grab your tinfoil hats.
Now the assumption was made that if Kaladin is becoming a herald then we would be getting multiple new heralds (and that laughably Shallan would be one of them). I dont think were getting multiple new heralds I think the existing heralds are going to die and were going to get one new herald and one champion-with-nine-shadows. If this is the broodiest time line-then they may both be Kaladin, but I doubt it.
Hell I could be wrong Kaladins new baby brother and family may be what he needs to heal during that year of time-skip while he sails around on his sky-ship with bridge 4 singing sky-shanties. Sanderson has definitely shown that he likes making Kaladin happy right?
*using this to refer to the things that torture the heralds not humans.
Edit: Almost forgot to ask, Why do you think Shallan is likely to become a herald? Other than MC status.