I'm not sure what this would achieve. I'm glad DD1 has gone into reception this year. She's born late march. Isn't the problem with age effect simply because someone has to be the youngest? And that the oldest in the class always have an advantage? I don't think, for example, the US starts school early. But they still have the relative age effect
en.wikipedia.org/wiki/Relative_age_effect
Here they referenced the statistics on footballers.
I'm not dismissing the issue where parents of summer borns are worried. I'm just glad that the choice is taken out of my hands for DD1. Otherwise I'd be unhappy she would be the youngest in her class being born on the last days of March! (So I totally understood the parents of late August borns).
I did my primary in Hong Kong where we don't start till 6. And I can tell you parents also want to delay start there. My cousin was an August born and his mum fight to be delayed one year. It has nothing to do with being too young at 6. It's just about wanting to be the oldest in the class. So he started at 7 instead.
DD2 is a early September born. So in effect she'll be in the middle of her class when she starts school.
I would definitely delay start my DC if she's born after April. Just because then she'll be the smartest in the class. I can afford to pay another year at nursery and I would do it happily.