I have visited this issue more than once and it is where the old knowledge would come in handy instead of us using trial and error. To have a reliable broody subflock, that you knew would go broody within a specific time frame in the spring would be invaluable to me, heavy large fowl preferred. I have heard of some breeds that more or less go off as a group, one goes broody and then the rest seem to follow. For now, I am resigned to having a long drawn out hatch that lasts into the summer. Combined with how long it takes my BR to grow out, I have a less than efficient process for selecting and culling my birds. Oh well! I'm not giving up free range or my broodies.
Me neither. Both are so valuable that they pretty much make up half of my whole flock paradigm. I'll never have a penned group of chickens for any length of time so as to separate flocks or breeding flocks. At the most I'll pen roosters before breeding season and occasionally for spot breeding sessions. No more chicks in the fall, though....I've learned the lesson on that one. Spring and summer chicks only.