Does anyone have any opinions on the Damn Secondary Hull Chasm?
I'd just like to point out that we don't exactly know whether it was there during the transwarp experiments yet. Since there are no stern views showing the hollow until ST6:TUC, we might speculate that the secondary hull was built "larger than it really need be" in order to accommodate machinery that was removed after the first few movies - either simply because the testing phase was over, or because the machinery had been revealed a failure.
Series production of ships with this now-useless cavity might still commence; plenty of real-world examples of such exist, such as armored vehicles designed
to take useless and indeed highly detrimental lead ballast merely because an early model was supposed to accommodate a wireless or an autoloader in the space!
The photographic model features an interesting greeblie in there, but this is virtually never seen. NCC-2000 features a blue "forcefield" glow, but this is unique to that individual vessel. And then there are the differences introduced in the "Flashback" model and the CGI models. Plenty enough excuse to think that the class was constantly being tinkered with, and that engineers well saw the utility of a "useless" expansion space.
I think you're onto something here, and I'll just piggy-back on it:
Maybe finding utility for this chasm (following the failure of the transwarp project) became a pet project of an engineer or two at SFC. Maybe pulling the original machinery/computers was time-consuming, and the affected Starships remained in service while it was ongoing. Maybe some of the ships had it turned into an open - and extremely well-lit - machinery bay. Maybe some others had it turned into extra bay for ancillary craft, with ONLY forcefield doors (no hardshell doors as it was not intended to be a shirtsleeve environment). There were probably what, 6-10 of this ships built at the TSFS/TUC size? Hell, maybe ship Captains of affected ships had input, and some wanted additional defensive capability, so they got uprated shielding components there, whereas others asked for and got beefier aft/amidship phaser/photon emplacements there.
Further, maybe some of the affected ships had the "chasm" closed off behind bulkheads, but we just don't see them.
Also, I haven't heard yet, but Praetor, this question is for you: are we assuming that the ship class from the TSFS and TUC is the same class as ALL the TNG ships?