DSC is a good forum for doing some long-awaited mixing. We finally have a broad combination of ship designs from the 1960s, 1970s and 2010s there (although TNG and DS9 already did a bit of 1980s/1990s mixing), with control interfaces from 1960s and 2010s merrily coexisting. In-universe, we may well be seeing different decades side by side, too. But none of it is fully explicit yet - nobody has stated onscreen the era from which the cylinder nacelles or the lateral vector transporters or the jelly button interfaces would hail, or the day these became outdated, or the exact selection of gear that is brand new for the 2250s. And perhaps that's for the best. But I hope DSC won't be limited to showing "DSC era" stuff.
I don't think that that's particularly likely (at most, we might see some more Constitution-family designs like Mirandas and the FJ configurations). The people making the show don't seem to be big tech-heads, nor do they seem to have delegated the "make everything make sense" job to anyone behind-the-scenes the way the way the 90s shows had a stable of Treknology experts, so I can't see them spending the money to recreate the Kelvin-family designs even though they logically should be around, in some form, at some scale, rather than using what they've got or making something all-new. I don't think they've ever used anything from the movies, or even earlier productions, as a time-saver or reference, whether design, graphic, or prop, aside from a handful of icons. They don't even use the right (by which I mean, post-TMP and thus wrong) font for the ship markings, just straight, unoutlined Microgramma without the shortened "1" that doesn't look so much like a "7," or the tails on the "D" so it doesn't look like an "O" or "0."
Personally, I don't see a problem with the three nacelle designs we've seen on DSC being contemporaries. They had multiple engine-styles in the TNG era side-by-side, and it never seemed that, say, the big round nacelle cap was necessarily more or less advanced than the small triangular red windows on other ships. Some ships get big flat nacelles like the Shenzhou, some get cylindrical nacelles with boxy casings around them like the majority of the DSC ships, and some have naked cylindrical nacelles, like the Enterprise. They all probably have merits or drawbacks, and are chosen based on the mission profile of an individual class, if not an individual ship.
Of course, that'd be a lot easier to sell if we'd actually see all the different kinds of ships Starfleet has together, instead of like always going with like. It reminds me a bit of the Halo franchise, where everything was redesigned to a greater or lesser extent for every game (and typically explained in the lore as being different models of the same line to rationalize the differences in look and performance), but they'd keep things simple, and rarely to never have two ships or weapons or suits that'd serve the same purpose show up at the the same time. The sort of verisimilitude of seeing, say, two different classes of frigate side-by-side would be left to books, comics, direct-to-web short films, tabletop wargames, what have you.
