If I am playing on the highest levels of MP and doing well then my skill level is pretty high. As a reward for that as well as having the stones to take on the hardest difficulty the game has to offer I should get rewards to carry over if I ever choose to play through the story once or twice. I have some suggestions.
1. If we are just a random military person we should be getting a paycheck yes? We should get additional money every pay period for being elite over just your run of the mill squads. Quality over quantity.
2. There should be romance options that are only impressed with the top tier of sexual beasts. Holding a leader board spot will really get their attention.
3. Some of the unique abilities or items that MP holds should be able to be transferred to SP as an elite soldier and someone that has used and mastered challenges associated with them in the MP. These challenges should be difficult to complete.
4. If there is PVP we should be able to take the loot of other players as we have our way with their corpse.
5. We should be able to call in support from MP characters who are leveled up as a nod to the best of the best to help through SP battles and give them some intense flavor. Also say hi to our favorite characters while we are not playing them.
I have some counteroffers, I think they are more fitting to someone with your level of "skill".
1) The best you perform in MP your gear/weapon/abilities get nerfed up to the point that when you're at the top of the MP ladder it is practically impossible to overcome the challenges of the tutorial fight in the SP story, and then you spend hours and hours dying for unknown reasons in what the "casuals" overcome in the first 10 minutes of the game, also your playthrough skips automatically all cutscenes, decisions, dialogues, romances, etc and you reach a default ending. These are the reasons why someone would play the SP campaign isn't it? Why that would ever appeal someone as good as you are?
2) When you reach the top of the MP ladder you get a coupon to play the MP shooter franchise of your preference for free, either "Call of Duty" or "Destiny" or "Halo", etc. and your ME game is locked until you reach the top of the ladder in these games as well. That would be a challenge fitting of your skill. Who is going to waste time playing a story-based game anyway?
I think that you would support my proposal