So in other words, you're contending that the module is the transwarp drive system, which was in fact successful and later revised for other ships into something less... modular? But for the Excelsior class, they had to remain with this odd semi-vestigial modular weirdness?
I believe the transwarp drive was only a large module aboard NX-2000. If the 23rd Century transwarp failed, the module was discarded, if transwarp worked, they came up with smaller components and integrated those into the Excelsior Class. Either way, the chasm became available for other applications.
Why can't there be other drydocks? (This is something I've always assumed to be the case.) In Generations, we see an apparently larger one inside of which the Enterprise-B was built. Perhaps it's the same one in which the Excelsior was built?
Frankly, it's the weird astonishment of the bridge crew at the start of ST III that made me wonder. Have they not seen the ship in drydock before, don't they know she has an experimental transwarp drive?
Why even bring her from the drydock inside the spacedock? Kirk's Enterprise
departed twice from drydock, Harriman's Enterprise-B
departed from drydock, only Excelsior
Of course, Earth Spacedock is shielded from curious eyes and that quarter section with the Excelsior may have been a restricted area,
hence the bridge crew's surprise.
Maybe it was a deliberate decision to have the Enterprise anchor there and thus withdraw her from public attention and scatter the crew USS Liberty
(the real ship) style.
If you seriously come to think of it, Kirk's career was heading for a dive. Somebody had to answer for what happened in ST II and considering all the lives lost under Kirk's watch because of his negligence, not to mention his naive and personal vouching for Dr. Marcus' Genesis Project, I can't help but feel that Captain Styles' threat was as empty as you could possibly imagine.
Shall I continue...?
And, I've never considered the possibility that Rand was on Excelsior,
especially given we see her in San Francisco in the next film. I always assumed she was assigned to Earth. Then again, in TSFS she appears to be a Commander, so she might have a twin sister.
She was a bridge officer aboard Excelsior
in ST VI and I think she had been on that ship from day one with that lounge in ST III having been reserved exclusively for Excelsior