The Last Levels of Champion Mastery

I'll be blunt, I'm a sucker for achievements. I loved it when riot added champion mastery into the game, because not only did it give me a way of showing how dedicated I was towards certain champions, but it also gave me another goal to work towards outside of gaining elo in league. So, with the recent addition of missions on its way I believe many people already realize that riot is most likely going to pair specific champion missions with the next group of mastery levels. It is a nice fit and a good solution to the gating problems that the previous two levels had. ( I.e. for the most part, it seems that most people had more trouble getting blue essence for level 6 and 7 rather than getting the champion mastery tokens themselves) It should be a very nice solution because now instead of just making players get a letter based on everything you do in game, they can see if players are truly hitting the top marks in every aspect of their champion with the added bonus that these missions can be individually tailored to each champion and role. ( so supports won't have to get X amount of kills to get an S+ ;) To me it seems pretty straight forwards what Riot should do for the next champion mastery levels.

However, I believe that Riot should make these last few levels extremely challenging. And, I'm not talking about a grinding time consuming challenging.. I believe that the next levels should really ramp up in difficulty. Like for example level 8 one of the quests for a laning champ would be play 5 games with 10 cs per minute. Not too bad, doable but still not an easy task. Level 9 however should be something like 10 games with 10 cs per minute and a perfect kda. And for Level 10, they should really make this one the end all be all. Make it 20 games with 10 cs per minute perfect Kda and preformed some stat indicator for your role better than 95% of other players. ( what I mean for this is for example a tank, lets say Malphite would have to have tanked more damage than 95% of other malphite players on average for that game length, They already do this in order to get an s+ score but I'm not sure what the exact numbers are)

I suppose riot could just go the 4 S+/5 S+/6 S+ for levels 8/9/10 route, but from what I've read other players want these levels to actually indicate that they have mastered their champion. I just think riot has a really great opportunity to use missions in a really rewarding way for players that want to show their mastery.

Anyway, I would love any feedback, or if you think that what I suggested is just too much! I know I'm really looking forward to whatever Riot decides to do with this and I'm curios as to what everyone else thinks!