I appreciated it as an effort to get away from deisgns that were at least 80 years old by the TNG time frame. I'm all for extended lifespans for Starfleet ships, but having half of any given CGI fleet in DS9 be made up of Excelsior and Miranda class ships was unsatisfying to this particular nerd...
It was unsatisfying to this nerd too.

I could understand why those designs were made into CGI, since they had the physical models to scan. But why have so darn many of them? Besides the FC ships and the GCS, these two classes made up the bulk of every DS9 fleet scene we saw.
It would have been nice to see stuff like New Orleans, Niagra, Freedom, etc. as they are more recent designs, but I also can see the producers specifically asking for designs that don't at all resemble the classic round saucer + cigar + two nacelle design quickly associated with the Enterprise.
Again, it was probably easier for them to just scan the physical models they had instead of building new CGI models of the New Orleans and Niagara from scratch. Plus, I always got the feeling that even though the BoBW kitbashes are technically canon, their use in anything other than that one episode was frowned upon.
What are the rail-looking things on the top of the Norway nacelles? Do the nacelles slide back and forth similar to how Intrepid nacelles rotate up and down?
Since we know virtually nothing about the ship, that question will probably never be answered. I suppose someone could contact Alex Jaeger and ask him, but I'd bet even he probably wouldn't know.
Because its the Ford truck of Starfleet, they get everywhere and do everything
Why else would they keep the class going if its wasn't up to the job?
Unfortunately, there's no good real-world explanation as to why Starfleet would keep producing an outdated design while at the same time producing more advanced designs. It makes no sense (and this applies to the Oberth class as well).
This conundrum exists because the producers of TNG were forced to re-use the movie models because they didn't have the foresight to build other new Starfleet ship models when TNG was being produced (and they also didn't want to spend money building new models if the show were to be cancelled after the first season). The only "new" models built for the show were the Constellation, Ambassador and Nebula classes, and only the latter survived long enough to be converted into a CGI model for DS9. But because the Excelsior and Miranda models were feature-film-quality, and the Nebula was only television-quality, we saw much more of the former two ships in the battle scenes.
Point being, that NONE of them could be easily mistaken for the Enterprise-E with the configurations we saw, no matter how tiny they were or fast they were moving. They didn't look like the hero ship, which is usually what the producers want to avoid. You'll note we didn't see any Excelsiors, Ambassadors or Galaxy class ships in the mix.
That was exactly the rationale behind the designs. They didn't want them to look
anything like the Enterprise because they didn't want to confuse the audience.