I really don't see the "contemporary" thing at all.
* The Akira has this round saucer just like the Galaxies and Nebulas that are her closest registry-mates.
* The Saber and the Steamrunner are their own distinct thing, down to having an all-new hull color.
* The Norway is very distinct from the Sovereign in almost every respect, too.
In addition, all have nacelles with the TNG style single-dome forward "ramscoop" and a neatly rectangular cross section; most also have the lateral "field windows" familiar from TNG.
I doubt any of these were intended to represent "new" starship design. Starfleet simply wouldn't have come up with anything new, and certainly nothing that worked well against the Borg - as having efficient Borg-killer ships would rather defeat the dramatic purpose of this fleet! Instead, we see especially Steamrunners drop like flies...
What these all ships could be is warships. From back in the days of the Border Wars, and having little to do in the peaceful years of TNG but float around starbases and wait for the next war. The ones with odd-shaped hulls would be dedicated combatants and therefore very distinct from the exploration ships of the heroes; the Akira could be sort of halfway militant.
Timo Saloniemi
I respectfully disagree.
Yes, the Akira has a more Galaxy-like saucer, which is why I said it had the look of something in between the Galaxy and Sovereign. Looking at the Akira and Steamrunner, they have some rather hard, sharp angles (especially around the nacelles and their struts), as opposed to the soft ones seen on a Galaxy.
So, it is possible that these ships could be newer designs.
As for the low registries... well, those weren't entirely consistent, though it would be nice to know that by the time Voyager was launched, it was their 74656'th starship built to date... and conceivably, they'd have at least between 50 000 to 60 000 ships in service by then - lower numbers of say 10 000 to 20 000 for 23rd century Federation might work ok though.
The higher numbers in the 24th century could take into account advancement in ship construction (speed-wise) as well as the overall size of the Federation.
Remember that SF is an exploratory and defensive arm of the Federation... not a military.
I would imagine they might think they have enough ships for defence... which could work with TOS Warp speeds of 990 Ly's per 12 hours, and ST V's roughly 10x increase on that speed (taking Transwarp into equation).
And if TNG, DS9 and VOY are set in an alternate reality with slower propulsion, then one could conceivably see Warp 9.2 as shown in Season 1 of TNG as being over 15 000 time c. Which would allow for 'reasonable' travel times across Federation space in just over 6 months time. Couple that with a trip back, and... yes, that 'could' work (allowing you to go from one end of Federation space and back in 1 year)... especially if most ships in service by that time could push 16 000 times c consistently... which could be Warp 9.4 (if we take Tom Paris's statement of Warp 9.9 being 21 473 times c - and subsequent incremental increases yielding doubling in speed).
Having that many ships is actually not unfeasible. Consider that for every ship not exploring the edge of known space or patrolling the Neutral Zone, there's a several more with far more mundane duties well within Fed space. There's vessels conducting scientific experiments (pretty much every Oberth class), testing new technologies (Pegasus), training cadets (Republic), supplying bases (Lantree), serving as transports (Jenolen), or holding vessels for surplus depots (Tripoli). Not to mention that runabouts and many other small ships like Data's scoutship from Insurrection have registries as well.
An "alternate reality" is a bit much. Apparently, it was simply a case of the warp scale being recalibrated between series because Roddenberry wanted Warp 10 at the absolute theoretical limit. It was likley a simple case of official forms of measurement being changed, like Daylight Savings Time or shifting to the metric system.
I don't recall that the Akira, Steamrunner and Sabre had low registries.
Though, if they did, perhaps SF classified them as lower registries because of being initially conceived as part of a 'battle fleet' (which might be counted as a separate task force compared to other ships in service that usually serve as a defensive and exploratory arm of the Federation).
Or they could be older designs which came out shortly before or during the 2360-ies - could have been launched with the Nebula class.
The registries of the Thunderchild, the Appalacia, the Yeager, and the Budapest are all considered sufficiently canon by the standards of Memory Alpha.
And as I explained about, they didn't really look that old.
It's my opinion that the four starship classes seen in FC were meant to represent Starfleet's newest ships, right alongside the brand-new Enterprise-E and the somewhat new Defiant. Yes, some of the ships have attributes from the older Galaxy class, but for the most part their designs evoke a newer lineage. Even the underside of the Norway class is taken directly from the Defiant's CGI mesh.
As for the low registries? I'm also of the opinion that whoever gave them those registries was under the assumption that they were the highest known. The same mistake happened in VOY's "Message in a Bottle," where the brand-new Prometheus class starship had a 5XXXX registry on the ship itself, while its dedication plaque had a 7XXXX registry. In that case, there was a miscommunication between the VFX department (who built the CGI model) and the Art department (who made the plaque.) I'd bet that was the case in FC too.
How to rectify this discrepancy? Well, registries have never been canonically shown to be chronological, so we could get away with saying a brand new ship could have a registry of 5XXXX if we wanted. Or we could say that registry blocks are assigned based on certain factors (i.e. the shipyard used to produce the vessel in question, or registry blocks of 5, 6, and 7XXXX are all ships built under a specific contract, etc.)
The Prometheus registry was a mistake (like the 1305-E for the Yamato), due to the guys who made the CG ship and the Okudas not being on the same page (the registry on the dedication plaque is much more appropriate).
They never explicitly said they were chronological, but there's enough anecdotal evidence for that assumption to be pretty reasonable.
In the 2160's you had ships in the low hundreds (the Essex in "Power Play" was explicitly said to be NCC-173).
In the mid-2260, you have ships in service in the low thousands. The Enterprise, launched around 2245, was 1701. The Excelsior, launched in the 2280's was 2000.
A century later, in the early 2360's, you have the first Galaxy class ships being launched. Setting aside the Enterprise-D, you have ships like the Galaxy, Yamato, and Odyssey with registries in the 70xxx to 71xxx range.
Ships commissioned around the 5th or 6th seasons of TNG like the Sutherland or the first runabouts have registries in the 72xxx.
Around what would've been the 8th season (or DS9 season 3 and Voyage season 1), we see new ships like the Defiant and Voyager with numbers in the 74xxx. Around DS9 season 6/Voyager season 4, we see the Prometheus, which, if you go be the number on the plaque, is in almost into the 75xxx, and the following season, you get ships like the Insurrection scoutship and the Sao Paolo which DO have numbers in that range.