Doctor of Credit just broke the news that Citibank is now restricting signup bonuses to one bonus per 24-month period in which you’ve opened or closed any card within the same brand (e.g. Citi ThankYou, American Airlines, Expedia, Hilton).
To restate this with an example, if you are approved for a card such as the Citi ThankYou Prestige, which earns ThankYou points, you will not receive the signup bonus if you’ve opened or closed any other card earning ThankYou points (e.g. Citi ThankYou Preferred, Citi ThankYou Premier) within the past 24 months. The same rule will apply among cards earning American AAdvantage miles, Expedia points, Hilton HHonors points, etc.
The only silver lining so far is that personal and business cards are treated as separate brands, so you could apply for AAdvantage-earning personal and business cards within the same 24-month period and receive signup bonuses for both.
Going forward, it appears that the best strategy for Citibank will be to cancel any cards you plan to churn as soon as you receive their signup bonuses.