It's done on RUT9xx, but not yet fully tested. I can see that it's still under development for RUTX.
Anyway, in both cases there is no due date as it is not a high priority project. So, I can't say when it will be out exactly, but it will most likely not be the next FW release for either platform.
If you also have a RUT9 router(s), best I can do for now is offer a test version of the FW with Wireguard implemented. (As I've mentioned previously, it's not yet fully tested, so it might be buggy, but it could give you a chance to try it out to see if it suits your needs.)