Aaron Forsythe said as much a few weeks ago on Twitter, but today is the official announcement from the Wizards Play Network that not only would Extended be added to FNM as an acceptable format, but also add Block Constructed.

This means that the following formats can be registered for FNM events:

• Standard Constructed
• Booster Draft
• Sealed Deck
• Two-Headed Giant
• Extended Constructed
• Block Constructed

Official source.