So nowadays you can basically hit lvl 7 on any champion you want pretty easly by spamming normal games with it. I'd like to see more Mastery levels.
I think it would be cool if Riot would add an 8th Mastery Level, that you would be very hard to achive. For example you would need 4 Mastery 8 tokens and 10k BE. And in order to get a Mastery 8 token you would need to score a S+ on that champion. I also think you should get some rewards for crafting it. Like a default skin chroma (like in Paladins if you've ever played that), or maybe a special Loading Screen Border for that Champion, or maybe discounts for the skins of that champion (yes Riot this would make you some money).