We've went round & round on this forum before, so I probably shouldn't even fan the fire, but,
You really want to keep this in-house, no matter what you have to do...come to an agreement to keep this in-house. period. All of these other reasons are just short-sighted excuses in great times. Much more difficult things have been overcome. You really do not want to rely on promises on a piece of paper.
How about this, kind of the FEDEX model: You have two hiring streams, At the interview you state whether or not you want to be considered for the ATR. If you take the ATR you are seat locked for 3 years and will not be entitled to by-pass pay. If you do not take the ATR you will wait for a "jet" class and cannot be forced into a t/p. If you have less experience, waiting for a "jet" class could mean you are never selected because you are going up against the entire pool. Nobody would ever be forced into a t/p. FEDEX is currently doing this more-or-less with their China and Germany bases and United has something similar for Guam. (as far as the bases being all-volunteers)
You want to rely on a scope clause in your contract?! In the late 90's AA's scope was that AA regionals could only fly a total of 75 jets with language that protected AA pilots from any aircraft that was currently on or invisioned in the market. At the time the smallest jets invisioned were the CRJ and the ERJ's each with 50 seats, so in theory the "Eagles" could have RJ's but only 75 of them.
I'll give you a hint, the fact that there is 44 seat ERJ (EMB-140) demonstrates what I am talking about. Ask HA25 what the AA scope clause said when he left. (before or after bankruptcy, it doesn't matter). When I left it was only getting worse, and I have no reason to believe the trajectory changed.
Scope clauses don't go away, they fade away. Everything is going well right now but imagine it wasn't (and there will come a day when it won't be) and the company comes to the HA pilots and say you have two choices, A: preserves your scope, it requires us to close the Maui hub and retire 5 717's, or choice B, you grant us "this one exception" to your scope, you let the ATR's fly off-peak HNL-OGG, Total ASM's will be slightly lower than required, and we only have to retire 2 717's saving 3 airplanes worth of jobs.
What's it going to be? Obviously, the choice will be B. And every few years, a little bit here, a little bit there.
No matter what you do, how it's structured, there is going to be a group of pilots flying 5 ATR's to start, for low pay and minimal benefits when compared to HA mainline. There isn't anything any pilot/union can do about that.
The question thus becomes, do you want these 50 or so pilots, on the inside, working with you, with an interest in what is going on for all the pilots at HA because they to are HA pilots? Or, are these pilots on the outside, where you can only hope they will do the right thing. Are they going to have an interest in doing the right thing for the HA pilots when the time comes, or are they going to be acting against you with their own self-interest. Will HA-Express be gaining airplanes while HA is losing them?
The only thing worst than being furloughed is being furloughed and seeing hiring and quick upgrades at your airlines "other" airline.
All of the other major airlines have spent the better part of the last 20 years trying to put this regional scope problem "back in the barn", trying to claw back flying. This is truly a unique opportunity for HA pilots, I hope you don't let it pass you by.