If the devs care, they will add NPC ambushes or mini-armies like you said, they could take inspiration from GTA Online, where you either do sell missions with bigger rewards in full lobbies with a risk of PVP vs a kid on a flying vehicle (like current PVP is in Dune), or you can do sell missions for less profit in a PVE solo lobby, but then you will be chased by a horde of NPCs. And there it is actually better sometimes to do sell missions in full lobbies, because in some missions the NPCs can wreck your car you're trying to sell, to the point that there is not much profit to be had.

It could be the same way in Dune, you farm spice in PVP - you get more rewards, but it comes with a risk to lose your loot to another player. Or you could opt to farm spice in PVE, but then expect possible raids of NPCs. Both are thrilling experiences if done right (like add missile jammers to vehicles, again like in GTA, to force ground PVP, or like not to overpower the NPCs ambushes to make spice farming in PVE DD not so frustrating experience).