for a new Ravnica set, we could see something like:
BLOCK 1
1. 3 guilds' cards, big problematic event happens
2. 4 guilds' cards, event is resolved but with unresolved fallout
BLOCK 2
3. 3 guilds' cards, plus 1 new faction is introduced that this block is based around. new issues arise because of the unresolved fallout and a new disaster rises. cards released for other guilds amend their mechanics to show how they're changing under this new circumstance.
4. the new disaster is dealt with. no new guilds or factions appear; the cards released further the already-established themes.