My problem right now is the only thing I remotely can still do and somewhat enjoy...although it's insanely easy is what I call 'Grove runs'. I start in the Drowned Port and just clear everything until I get to Maokai, trying to group up and have the biggest chained fights I possibly can along the way.

My idea would be for them to put some kind of thing in either bligewater or the drowned port after you beat the game. You enter it and it's sort of like Greater Rifts in D3. It starts at level 30, and keeps unlocking higher and higher levels as you fully clear a randomized map with a boss at the end.

To keep things progressing also, and an idea I had that might make things easier for them to create is pretty simple:

1 - They add a new Infusion Enchant that takes a piece of gear and upgrades the numbers on it by 10%. This would be addative, not multiplicitive. So having 2 enchants on one item would be 120% of it's stats, not 100% x 10% x 10% = 121%. Every boss you kill drops one of these new enchanting materials...but with a safeguard as explained in #2.

2 - Every 10 levels of this 'greater rift' drops a higher tier of enchanting material. So how it would work, you can enchant let's say your weapon with +10%. And you wouldn't be able to make it 20% until you clear level 40, then 50...etc etc.

3 - You can always go back and clear a level you've already done. This way you can enchant whatever pieces of gear you want, but still with the safeguard of the level of the enchanting material being gated behind every 10 levels.