only just read this post, but have been thinking similar. I do some hedge laying in winter which generates a fair swath of brash. want to have in the local unimog and chipper to have a go - no idea how much chip it might produce and would need him to call in when passing to keep costs down. my other thought, similar to yours, is that instead of regularly flailing hedges - leave them for say ten years and then someone invent a harvester to chip the growth and take them down to four foot again. if you did this rotationally around the farm you could have a good mix of hedge growth stage, and I bet one chipping wouldn't cost any more than five flailings plus you have the chipped material.
This is a good idea, flailing also means each years growth lands up in the bottom of the ditch leading to silting up and blocking culverts.
Chipping however is expensive and hard work. I have tried chipping brush wood from coppiced hedges for my composting and it took two of us all day to fill a 14 tonne grain trailer. Now I buy it in at £80 a load which is much cheaper and a lot less work.
I have made some huge piles of brush wood 5 years ago and just leaving to rot on its own. One day this will make a lovely material to add into the compost.