Belkin has been releasing code for OpenWRT on the Belkin WRT1900AC router going back to April when the router started shipping, but still it doesn't yet fully work with OpenWRT and requires binary blobs.
An update on July 30 reads, "I really hope this is the last update I post before the inital WRT1900AC wireless driver is released...Some users may be disappointed to learn that the release will contain a pre-built library. While this may not be ideal for some users, it is good progress and will allow for developers to recompile the driver as updates are made to the kernel. Going forward I am sure efforts will be made to incorporate a wireless driver where developers have access to 100% of the source."
A OpenWRT developer already responded, "Quite frankly, this is completely ridiculous. Belkin has already released the source code of this driver in a GPL tarball. Interestingly enough, the driver there has GPL license headers apparently added by Marvell. Having seen the driver, I can say that even with full source code available it would be hard to get it accepted into OpenWrt for a number of reasons." Among the reasons expressed include the use of a non-standard kernel ioctl rather than standard Linux wireless APIs, no support for upstream hostapd, and bad code quality.
At least for now, so much for the Belkin WRT1900AC being great for OpenWRT fans, unless you want to apply external patches and use a pre-built library.