The article is interesting - I had no idea so few (relatively) of the girls at GCH had EAL, since nearly all the ones DD is friends with do. Perhaps it's just her year! Since it's a language school, they prioritise those with an aptitude for it and the class that got highest marks in the test study 3 languages and most appear to be of foreign origin looking at the names.
It can be very hard for faith schools to do what's right: on the one hand, if they want to promulgate their faith's teachings, they need to feel sure the parents will support them, so it does tend to end up being a test of parents which felt unfair even at the time. On the other is tess's point - I think GCH's ability to bring the girls in from all over London is more likely to improve inclusion, not less. Westminster has a strange social mix, so it might be less relevant for them than for the Oratory, but I still think it's probably the case. For us, we wanted a faith school (why they get better results, I have no idea, but they mostly do) and DD wanted a girls' school, which only exists round here if you're Catholic. Her friends are mostly closer to the school than she is, ranging from literally over the road to the other side of town, and from a broad range of backgrounds as far as I can see.
I'm not sure I can see that removing the faith option will improve social inclusion that much for the country as a whole and I'm pretty sure it won't improve results. Still, I accept that's just my opinion.