Riot, A sandbox please.
I think there is a ton of creativity and flexibility in game modes and I really wish RITO would cater more to this aspect. Not just featured game modes that go away shortly and very fixed modes/rules. Make custom games have dozens more customization options. Let us be free to have the power to design. We might make some winners for you.
Custom item sets? Custom champ select lists? Custom stat boosts? Chimera champs with each-other's skills/passives?
There are so many ideas for what options could be available in custom games I could list for pages.
ARAM battle of nations pick a country(lore) and fight against champs of another. ex. Demacia vs Noxus Piltover vs Zaun Shurima Vs Bilgewater
Clash of titans Random person on Each team gets boosted stats and size and four remaining players pick champs from support pool. Help your titan win.
Tag team players are locked on base until player in lane dies then they are allowed out etc taking turns playing and cheering trying to set each other up for kills.
The more power we have to play with the cooler things will come out of it I guarantee it. It doesn't have to be a normal queue or give IP but..
GIVE US A SANDBOX
We will have fun in it, and you can use what we make.

I thought of something like this and wanted to see if any big posts weren't already going before i posted mine (1st time on forums) and i had a few similar ideas to what you posted and a few others:
Cdr/attack speed/ move speed/ life steal/ (etc) caps
move max CDR from 40% to a certain amount or change the attack speed cap to 5.00
jungle spawn and respawn timers (baron and dragon up at 1:55 for example, or blue buff every 3 minutes instead of 5)
Champion level and gold at the start - skip straight to a level, or start with 99999k for a quick full build
Possible to be customized for each map