The last missive from the SJRU that I saw, which only came out this week, said that they will definitely be running Saturday competitions this year. As Gary Owen III has said, this will occur in a 10s or 7s format if they can't run it as 15s.
IMO the SJRU need to forget about trying to accommodate private school players, all this does is alienate some of the boys who don't go to private schools. I was involved in coaching a 17s team in the northern zone back in 2000. This was the last age group that had gone through playing all matches at 2pm on Saturday afternoons. At the start of the season Northern Zone tried to get us to play on Sundays as that was when all the age groups below played. (I think a guy Spana ? was behind it) Anyway, I was pointed out to him that none of the teams involved had any private schoolboys playing and if the competition was moved to Sundays, then at least 4 of the teams would have to fold because a number of boys played league on Sundays.
The guy at Northern Zone backed down, but since then all games from 10s to 17s have been played on Friday nights or Sundays and I think from 13s up it's all Sundays. I can't help but think that there are non-private school players who would play in a Saturday competition, but who won't play on Sundays.
IMO SJRU need to develop competitions of their own, which don't rely on being propped up by private school players backing up from their Saturday school match and playing on Sunday. I was at the meeting back in the 90s when Northern Zone moved from playing all games on Saturdays. In the first season or two, matches were still programmed for Saturdays, but by mutual agreement they could be rescheduled for Friday nights or Sundays. So many games were being moved they just did away with Saturday rugby. It was done for the best motive; i.e. to keep teams viable and give as many boys as possible the chance to play. Long term, however, it's just made junior rugby the poor cousin to school rugby to the point where it can barely exist without private school players. Some clubs have just become lazy and instead of getting out and finding new players when school rugby starts, they just keep using the school players - which works until 16s, but then it all falls apart and it's impossible to find many new players at that age. Much easier to recruit players in 13s than in 16s.
There will be some short term pain here, but I'd suggest that they move all their games back to Saturdays, build a long-term, sustainable structure which should lessen the need for the best players to head off to the private school system. It's not that long ago that all Sydney junior club rugby started at 9am with 10s and finished with a 2pm 17s match. We don't have to re-invent the wheel, but we have to rebuild it and that requires some pain.