Im really skeptical of this.
Many look down upon XX breeding for fear of missing something from the male plant. If its so simple to force regular XY seeds to express as mostly/only females before germination, feminized XX seeds probably wouldnt be as prolific as they are currently because we wouldnt need them to make only female offspring.
It's not as easy as it's made out to be. That's for damn sure!
The only thing wrong with XX breeding is the tail at the end of the DNA (can't recall it's name) keeps getting shorter. That tail is restored with XY breeding. Otherwise I don't see any issues.