Luca Todesco has released a jailbreak of iOS 10.2 with a working mobilesubstrate.
Todesco posted the source code for the jailbreak last night and this morning has posted the first beta IPA.
Yalu 10.2 currently supports the iPhone 6s, iPhone SE and the iPad Pro. Support for additional devices will likely be added in the future; however, Todesco has said that the jailbreak will not support the iPhone 7.
You can download Cydia Impactor and Yalu 10.2 from this link.