I don't really understand why informed consent would be such a difficult issue for this new piece of research. Puberty blockers are already used safely for precocious puberty, so surely giving them (for an appropriately brief time) to older children is not intrinsically dangerous?
The danger, as I understood it, was not to do with any inherent risk in the medication itself. It was to do with the appallingly lax way in which they were prescribed, without appropriate screening, without exploratory talk therapy, without ongoing intense further exploration so that they could be genuinely a "pause" rather than the first step towards further medicalisation.
If all those failings were corrected, and if other boundaries were in place (say, a maximum of six months on the blockers, or whatever other short period the study protocols deemed safe), why would that create difficulties with informed consent.
I mean, there may be other problems with the study, other reasons not to go ahead with it - I really don't know. But how would informed consent be an issue?