Thinking about the idea of earning cumulative points per ET that carry over to the next one…
There could be 3, 5, and 10 targets. Maybe a higher number of playable (at once) ETs could be unlocked after earning so many points. I’m thinking of something similar to the Sniper Challenges. Yeah. Talking about grinding a bit. Or perhaps setting particular restrictions per target to meet a quota for advancement.
Let’s say you pick 5 targets that are all from the same area, such as Paris.
The Forger, The Broker, The Pharmacist, The Identity Theif, and The Paparazzo.
Next, you can choose Restrictions.
These could range from…
- KO’s allowed (this is the default).
- No KOs (instafail if any KO’s are made)
- Limited KOs (then choose, 1, 2, or 3) 4th would be instafail
- KO’s result in a -250 Point deduction, but hiding any bodies = +250 Points.
- Headshots Only
- No Loadout
- Accidents Only
- Use ______ (method) Only. They could be pistol elimination, lethal melee, fiber wire, poison, sniper rifle, etc. But this might not be a good idea since some methods may be impossible to use on certain targets.
So the restrictions/requirements could be worth small bonuses… How much? Well, there are passive restrictions like No KO’s. Those shouldn’t be rewarded. Maybe using Fiberwire or Pistol Elimination would give more. It’s about Risk vs Reward.
Speed Bonus? 
As I’ve said previously, For the first ET you’d get 1x (standard) multiplier.
For the 2nd ET, you’d get 2x multiplier and it’d be added to your previous score. And so on.
Although, such a system might need to have all the kinks worked out. Or it could be a matter of trial and error.