For me, I would be ok with a tiered system, where depending on the option you get more XP and crafting resources (I would also add back the feature from VT2 where each level up past 30 grants a new Emperors gift).
1.) VT2 style pick any mission/map you want on any difficulty. No secondaries, No modifiers. Base crafting + XP. Can be private.
2.) The Current map selection, with bonuses from secondaries and modifiers, but difficulty is changeable. Similar to DRG. Maybe private allowed here. Increase map rotation so finishing one match you are going to see new ones. Instead of maps changing out at random times I would do DRG style every ~20 minutes the whole screen changes.
3.) Quick play and select difficulty, prioritizes filling teams missing players. ~25% more crafting materials and XP. Private not allowed at all.
Why? Because fatshark decided to do dedicated servers unfortunately. If they kept P2P this would have been easy, but the servers can only host so many instances and allowing full choice increases server resources/costs and makes matchmaking harder.
So they obviously have an interest in keep map selection low and getting as many players to want to play PUB as possible, and I think the incentivize of grinding will make players want to do quick play enough, and those wanting to experience new maps have that as a choice.