"The first Anglican woman bishop to preside and preach in a Welsh Cathedral."

Details can be found on the Diocese of St Asaph website [here] 

There's an interesting piece of propaganda on the the same subject here
A 'threshold' has indeed been crossed ...

"Bishop Gayle was invited to the Cathedral by the Bishop of St Asaph, Dr Gregory Cameron, who will also attend the conference in Cardiff.
He says, “Women bishops have been a reality in the Anglican Communion, if not in Wales, for some time now.  It is good to be able to welcome Bishop Gayle into our midst to lead our worship in this time of transition.” 

And, on a related subject, rather than indulge in yet more pointless and wearying speculation, we will see exactly how many 'friends'  traditionalists have on the Welsh Bench 'in this time of transition' when the long awaited (and inexplicably delayed) Code of Practice is presented at the Church in Wales' Governing Body when it meets in Lampeter on 17th and 18th September.