Updated Arkham Sourcebook on the way
Chaosium confirmed recently in a marketing email that an updated version of the Arkham sourcebook will be released in February.
Dicebreaker has some details:
The new book will expand on the original sourcebook with additional options for NPCs, locations and scenario ideas. Arkham will be part of Call of Cthulhu's Arkham Unveiled series, with each book focused on a different place around the Miskatonic Valley. Chaosium said that the sourcebook will be followed by separate scenario collections set in and around the city, due for release in "due course".
Dicebreaker