No child who has been on puberty blockers and then cross sex hormones, with or without surgery is going to play rugby, or any competitive sport for that matter. Their bodies will be medicalised with all sorts of problems, and staying healthy and fit and out of hospitals will take a lot of work, let alone playing a sport as demanding as rugby.
Well yes, quite. It's not really the same as a top athlete having, say, managable Type 1 diabetes or something.
It does seem that, for a 'trans child' it is all encompassing both physically and emotionally. If you think about the amount of medicalisation it takes to stop a puberty from happening completely, the amount of medicalisation it takes to 'maintain' a biological male as a 'girl' and the effect that has on their body, the number of hospital appointments, the counselling, the emotional impact it all has on both the child themselves and their families (who normally in top level sport have played an enormous role in the athlete getting to that point) - it's highly unlikely that alongside all of this a child would develop a passion for and rise to the top of any sport really as well?
That's not to say that trans children or trans people aren't interested in sports or can't participate appropriately, but I'm just thinking the compatibility of top flight sport with a someone who didn't actually go through puberty, it's just not going to happen is it?