The Kingslayer format was required because one core of Thrones 2.0 couldn't make a normal tourney-legal deck. You took two factions, smooshed all their cards together in a pool, and added the neutral cards, and there you go, a deck of legal size, if not construction. I believe there was enough wiggle room with neutral cards that you could slightly deck build (by leaving out a card or three from one of the factions), but it largely was a deck with one of each in-faction card (except for the in-faction resource producers) and 2 of each neutral. Which, actually, is pretty much the learn to play decks in the box -- they're completely illegal (by normal rules) decks that use a single copy of two factions' cards along with two copies of the neutrals. I'm sure that's why the decks in the back of the Learn to Play book were referenced, as those were exactly the only sort of deck you could make.
As L5R will undoubtedly be single cards of in-clan, with perhaps 2 copies of neutrals, I am expecting a Kingslayer-style construction rules required for the first tournies at GenCon. You'll pick two clans, combine the cards together, add the neutrals, and play.
