Or, you accept the answer, which was posted already often: It's available when it's ready! Merlin is a one man show and does the great job on the firmware in his free time. Give him the time he needs and have fun when you get it!
RMerlin can only release new firmware based on what Asus releases (not just the firmware; gpl code required).
Asus seems to be concentrating on the newest Routers as they should be (RT-AC3100, RT-AC88U and RT-AC5300) in the last few weeks, not to mention their national holidays getting in the way. They'll return to the older routers when they can.
And then RMerlin will have a chance to do his magic after that bit of work is released to the world at large.
So, as joegreat already said; it'll be ready when it's ready.