And the Stargazer was a Constitution Class when the episode was filmed, but (according the the Encyclopedia) the producers decided to build a new model after it was filmed.
Hmm... Note that when the live-action bits were filmed, Picard's ready room had already been emptied of its tabletop
Constellation model, supposedly because it was needed as reference for building the full-size photographic model of the
Stargazer. So the decision probably was made during or just before filming, not after it - but in any case so late that some of the dialogue had been shot with the other class name. Whether this was because the decision had not yet been made, or because the decision had been made but nobody had gotten along to correcting the scripts yet, we don't really know.
The Enterprise-B kinda had to be an Excelsior: The Excelsior was the new biggest and coolest ship in Starfleet, taking over that job from the beloved Constitution Class.
To be sure, in ST3 the
Excelsior had been the villain ship. It was far from certain that she would ever become associated with the heroes: after all, her main design criteria for ST3 had been "looks buffoonish and intimidating, fails to deliver". She lived up to that in ST4, too.
Of course, by the time the E-B was shown, there had already been a change of plans and ST6 had made the
Excelsior, if not hero ship, then at least a respectable sidekick ship. And the first half of TNG had shown an
Excelsior class ship in the "lineage relief" on the Observation Lounge wall, supposedly marking the E-B (although the relief would turn out to have several inconsistencies in that respect, and others).
However, had the producers wanted, they could easily have invented an all-new class for the E-B. They'd just have to explain why this class was never seen in TNG even though the
Excelsior class was frequently seen and the
Ambassador class of the E-C was occasionally glimpsed...
On the issue of naming, there'd be pretty broad precedent by the time of ST3: "enterprise" is a concept, "constitution" is a document or perhaps a quality, "Lexington" and half a dozen others are battle sites, and "Potemkin" and half a dozen others are people. "Antares" is a star (literally "Opposite Mars"). Why wouldn't an ambition fit in that mix?
Majestic ships are named after stranger things in the real world. The masive fleet carrier
USS Shangri-La was named after a joke President Roosevelt cracked, on the basis of a popular novel of the time...
Timo Saloniemi