In cases of "extreme toxicity" (i.e. racism, death threats, homophobic remarks, etc.), troublesome players can expect a more severe penalty ranging from a 14-day ban to a permanent ban from the game. In the case that an "unfair ban" comes into question, Riot says they will now be fully transparent with chat logs and post the exact log that led to the player's ban.
Intentional leavers/AFKers are also a concern for Riot as they plan to address these problems in the future.