DSP is made in Unity, a game engine that very much supports multiplayer.
I've been modding this game for 7 years now, I believe it can't be done with the custom engine this game uses for very simple reasons (like non deterministic randomization, or aforementioned multiple gameplay layers and altered time flow mechanics). But hey, what do I know... However people smarter than me said so, and Alex himself said so too.
The closest to multiplayer you'll ever get is the coop mod, where under the hood you have a second player sharing your keyboard that can use shortcuts to order the AI of a second a ship to "turn left" "accelerate forward" or "fire your weapons". That's as close to multiplayer you'll get.