Too early to tell. At this time, one of the models fails to compile at all, and another crashes at boot time. The only two models I have tested are the RT-AC88U and RT-AC56U (which gets used for development/testing purposes).
And as it turns out, half of those recent GPL releases are missing the critical closed-source components, so for these incomplete models (which includes the RT-AC68U), I cannot do anything until I can obtain the missing bits.
That's why asking me if or when a certain GPL release will be merged in cannot be answered until I have actually tried to do it.