As of right now, Forge is not even on 1.13 (See this chain of tweets), so we have not yet been able to even start updating the mod. I've also heard that the update includes some major changes, so don't expect a 1.13 RM right after Forge is on 1.13, it'll probably take anywhere from a week to multiple months (depending on the specific changes and how much time we can put in it).
@User10 The forge IS on 1.13 now, just to inform http://files.minecraftforge.net/maven/net/minecraftforge/forge/index_1.13.2.html
But I know it will take some time :), I am also developing, but not a minecraft mod, just a webpage and it is also quite hard and it takes long to think of an update