After investing in digital verticals focused on business and politics and acquiring an online-video startup, CNN is gearing up for another big step: It plans to launch tiered subscription offerings for its digital news business as early as the second quarter of next year. A proposed premium offering will give subscribers access to special content on topic-specific verticals such as CNN Money and CNN Politics, built around network personalities. A second option will provide additional, though less specialized, content across all of CNN’s sites. Pricing hasn’t been finalized.