The Super/Shute drain is one of the issues here - if you're a young man playing rugby at school, you're aiming for Wallabies or NRL. Tahs may be a fallback in which case you bugger off to Europe or Japan if you get the chance at more money, but I don't think many kids are aspiring to play for district teams, let alone suburban clubs.
I think it plays a part - a bigger issue is school leavers not staying in the game IMHO.
How many schools in Sydney have rugby?
How many have multiple opens XVs playing?
That's the numbers game - knowing how many kids played rugby and are leaving school - so we can figure out how many are candidates for Colts.
Premier Clubs will not need to refresh their entire Colts program every year as someone are still U20. It will vary but if you put down 30 players per club, in Sydney that's 330 to get you started. I know a lot of clubs are bringing country kids in as well to help bolster their numbers, so it might be less.
As a Subbies club, I know I'm not getting the superstars so First XV guys and a lot of Second XV as well.
And quite frankly the 3rd XV prop at Oakhill who likes the idea of a beer and a game with his mates is probably more valuable to me
Local, social, and committed. If I got 6-8 guys per year coming through, they could run in Subbies Colts (U21) for 3 years while also supporting senior grades. The issue is getting the first squad of 25-30 together...
Depending on who is aging out, Subbies clubs in the top 4 divisions would need between 6-10 players each I reckon, which is another 200-320 players.
So for Premier Rugby + Subbies Rugby, we need about 550-650 kids every year, so up to 43 XVs.
Back to the questions: how many schools in Sydney have rugby? How many XVs will be leaving school?
AND
How many of them are staying in Sydney? How many kids can we find from other sources like League or Aussie Rules?