A major benefit of SDX might just be the ability to put in custom assets for the cool features you've already had in game for a long time. Some of the SDX mods I currently use will be in the vanilla game in one form or another come A15. Matite's Drawbridge, three08's Prison Door, three08's Secure Storage Containers, three08's Dynamic Sign, pjc21's Signs
There are a lot of cool SDX mods, but the multiplayer compatibility of their scripts is usually the first thing you have to check before you get too excited.
Hal's Chicken Mod is pretty neat. I don't believe it is currently compatible with multiplayer, but Hal said he might work on it for A15. As it is configured it isn't in line with your mods difficultly, but it is highly customizable. Definitely one to keep tabs on.
Carlzilla's Smart Containers is the best quality of life mod ever, it removes the tedium of storing everything away once you get back to your base after a loot run. Sadly, it is also not currently compatible with multiplayer. If this ever becomes multiplayer compatible I can't imagine anyone playing without it. Once you've created custom containers and configured the mod for your items and blocks the power of his script really starts to shine. I warn you though, do not test it in singleplayer too much because you will never want to play without it again.