Really simply suggestion that could bump up playtime for some players…
Give the players the ability to ramp up the missions for higher reward…
Example…
Tier 1 = Get 10,000 Support XP = 500 Credits
Tier 2 = Get 25,000 Support XP = 750 Credits
Tier 3 = Get 50,000 support XP = 1000 Credits
Tier 1 = Get 25 Headshot Kills = 300 Credits
Tier 2 = Get 50 Headshot kills = 450 Credits
Tier 3 = Get 100 Headshot kills = 600 Credits
By allowing a player too increase the tier of missions you encourage them to play longer for a reward that in the grand scheme of things is very low… 100 Headshots gives you the number of credits you would expect for 2-3 objective mode games but could encourage the player to double the games played.
On a side note I would also add a weekly Mission based on their preferred play style to encourage them to continue playing what they are good at and advance to / buy new mercs… Have the weekly missions change on a Sunday but Merc rotations to change mid way though the week.
Example…
Get 250,000xp with Proxy = 2500 Credits OR skin/craftable.
Personally, I just think its a good way to reward frequent players and encourage less frequent players to play a little more than normal without forcing them too.