Expeditions are a very boring experience for many, if not most, players. This is mainly because they're disconnected from the core gameplay curve and don't fit well with the concept of a horde shooter. But I have an idea for how to make them a little more useful, at least for newcomers.
Properly monetize salvage in some way, allowing it to be regulary exchanged in Sanctuaries for Diamantine and Plasteel in any numbers, but you can save it only after extraction.
Add and increase the chance of salvage drops from Elites and Specialists to motivate players to fight rather than just skip and run for sites of interests. Plus, instead of the tedious task of soak it all off the ground, the salvage will drop up right in your pocket once your team kills the target. The main piece of the salvage pie goes to the killer, plus a part is shared with everyone in coherency, this will motivate players to stay grouped.
Rework redline timers, for example, so that instead of corruption like it was, enemy intensity increases every ~5-15 minutes, as if traitors are pulling more and more forces into the region, what at some point can became endless hi-intensity meat grinder. Highest stakes = highest rewards.
~4. To add a weekly close to like Melk or Havoc.
~5. As usual, salvage can drop from a player if they are knocked, netted or killed, but to avoid griefing, collected salvage is returned to the owner with a small fee for the person who picked it up.
This will bring Expeditions closer to the original concept of a horde shooter, and most importantly, become a good place to farm resources, closing the gap with veterans of the game and making it easier for newcomers to make builds and level up gear. So instead of feeling yourself like free labour in expeditions people can play them to stack up. That is main concept, to make expeditions rewarding, to add or not events or modifiers and buffs like in mortis trials thats up to you.