these are my ideas, i hope you will like at least some of them
1) Button to autofill custom games with Beginner or intermediate bots so you won't have to add them one by one.
2) Option to disable skins or at least change visuals and sound of their spells to their basic forms, because some skins make certain abilities worse to notice.
3) Make it posibble to use old champion splash arts, you could make it a reward for leveling through mastery system. The same thing could be done for old summoner icons (I miss my teddy bear :]).
4) Add Damage Absorbed/Prevented chart to post game stats.
5) Add voice chat, because typing isnt realyl necessary since we have pings, and we have timers for camps.
Having voice chat would also make the text chat less clumped and over saturated with non sense messages.
I consider myself a slow writer and because of that, i cant really shot call for our team which i could do with the implementation of voice chat.
6) Add number of key fragments obtained since last reset and option to see when is next reset going to be.
Thanks for reading.
EDIT: I can see that many of you are concerned about the negatives of implementing voice chat and i have to honest i thought about it too. Having voice chat in normal games/ fun modes could be more negative than positive, but when i play rankeds in high plat/ low diamond it would be extremely good (at least for me) to have it. Most of the players in ranked actually want to win and not argue. There could be a button in dynamic queue to choose if you want to play with voice chat enabled/disabled. It would be optional under Platinum or even diamond, and from diamond up it would be enabled by default, since there are less players and it would be a nuisance to split them into two different queues.
EDIT: TL/DR: Voice chat could be implemented only for ranked and would be optional in platinum or lower.