On fallback systems in the 31st century

I was watching the newest episode of Star Trek: Discovery when they said "the port nacelle needs repair". This proves that even in the 31st century, ships still needs repairs from things that would damage them the same amount it would in the 24st century ships when you'd think they'd have improved their shields by now — but it did make me consider something.

Consider this: a cycling system for the nacelles. The ship could carry 6 or more nacelles, and swap them out at any point. That way, if a nacelle gets damaged, they can swap it out with a fully functional one. They could carry the nacelles in either a triangle shape carrying 2 extras on each side, or carry any number of nacelles on the underside of the lower part of the ship.

Of course, "lower part of the ship" refers to vessels like Discovery or Voyager-J that have mostly flat bottoms. There's also ships like the U.S.S Nog (Memory Beta link), which have a pointy bottoms. On ships like this they could either go for the triangle approach, or find another place — like the back.

Similar ideas could apply to other areas of the ship. Perhaps even entire sections could be carried as back-up, like a second secondary hull.

It's worth noting there is absolutely nothing in-universe to prove this is even remotely possible. There still seems to be a lot of variety in ship designs. If you compare Book's ship to Voyager-J, you'll see what I mean. That would step in the way of just swapping sections between ships, but also make it harder to engineer these sections en masse.

The Federation is also in a fairly tight space, where they don't have the engineering capabilities to build reserves of anything.

Of course it will be greatly interesting to see if the writers decide to do anything like this. Even if ships don't carry reserves or hot-swap sections, something like hot swapping nacelles would seem fairly reasonable.