If the main issue is having Redbacks players not having a game of cricket to play if their club has the bye, why not just allow these players to play for another club on that day? That is then technically creating a stronger competition instead of weakening it by adding an U19 team.
Which club has the most state squad members? Doubt any would have more than 3 or 4. Just place them in the bottom teams for that day (I.e. If there are 4 players without a game one each gets added to the bottom 4 teams.
It's a strange set up when you have futures squad players currently playing B Grade to ease their workload yet at the same time going through and trying to cull a successful club to ensure these same players are playing enough cricket.