According to the latest information shared by Mark Gurman, a previously rumored 12-inch MacBook with Apple Silicon won't be released this year.
Gurman did not reveal any more information about the 15-inch MacBook Air, but display analyst Ross Young previously claimed that Apple's suppliers would begin production of 15.5-inch display panels for the new MacBook Air in the first quarter of 2020.
It's likely that the 15-inch MacBook Air will have the same design as the 13-inch model, and it will be available with either M2 or M2 Pro chips.
Lower-end and higher-end 12-inch notebooks have been released by Apple. An ultra-thin 12-inch MacBook was introduced in 2015, but it was discontinued in 2019. The original MacBook Pro was preceded by the PowerBook G4 in the mid-2000s.
An ultra-thin, fanless MacBook could be reintroduced by Apple if it ever decided to do so, since Apple's Silicon has superior performance per watt.