It will be drilled at least 5" . Carbon fiber tube will be used for tenon.
New lightweight but durable ferrule will be installed. Carbon fiber pad will be added.
The same length as your ferrule now. Less if you don't mind the shaft being a little shorter .
Premium tips are extra of course .
The shaft will lose at least 1/10th MM in diameter up front.
No, I don't think I would.
Hollow shafts always hit hollow. Never seen an exception to this rule. The shaft won't feel solid and the reduction in deflection will probably not be consistent from shaft to shaft. After a while you start to recognize the weak and "clicky" hit from a hollow shaft. It may not strike you in the beginning, but after a while it starts to bug you (or at least it does me). Predator Z's are the prime example. After a while you begin to recognize this hit in all hollow shafts. Some are better than others, but it can never quite be masked. There's no getting around it, unless you use carbon fibre for the whole shaft, which has other problems.
I might pay 150 dollars for a shaft that has been made like this just for an experiment, if I get to try it first. Maybe even 200 dollars if it was extremely well made. It would have to beat the McDermott G-core at the very least and at least be on par with a Predator 314 to be worth considering. Don't forget I could get a used but nice Predator shaft of my desire for probably around 100 dollars at the pool hall, whenever the next sucker gets tricked into buying one of their 500 dollar wonders. Makes it hard to want to take a leap on an unproven (to me) concept that may be a huge disappointment.
But there is no way in hell I'm paying you (or anyone else) 75 dollars to potentially ruin one of my shafts. My experience with cue repair people is less than stellar. "My lathe exploded". "My dog's getting puppies". "Religious holiday" (of course the excuses are not quite this silly, but after a while they begin to sound like that). Meanwhile I'm waiting 1 year on a refinish...
I wish you good luck, but if I were you, I'd buy blanks and sell ready made shafts. That way you won't have to explain why the customers favourite shaft got ruined (by accident in the lathe), or just underperform in that persons opinion. If you proceed, I hope you have good nerves....It won't be fun having to replace 3-400 dollar shafts from near impossible to source makers...Unreasonable people are found on both sides of the counter. Some customers are just impossible to please. Maybe it would be better for sales to charge a premium price, like 300 dollars or something. People are suckers for expensive "custom" products.