Replace Treeline with Nexus Blitz
Yes some of the events were way over the top and it would need some balance changes but having a game mode you know will end before 20 minutes that is somewhat similar to SR was not the worst idea.
If a game was going badly it would be over before 20 minutes basically always. It was actually decent for working on learning a new champ because it had enough similarities to SR with less of a time commitment should things be going bad so you can start fresh instead of spending 25 minutes jsut trying not to feed.
I can't remember the last time I played on treeline and most people seem to stick to SR and/or ARAM. Nexus blitz was kinda a middle ground between the 2 having the faster ARAM pace, while having more of a SR style map where you can pick your champ but still being 5v5 where a meta was starting to form but nothing seemed to be completely useless.
If looking for "fun" game modes Nexus blitz beats out treeline hands down. It did not come across as a serous game mode but it did have enough of a skill factor to make it feel worth trying to win and if you lost you could blame it on bad events for your team comp.
And yes I would likely replace most my solo ARAM play with Nexus blitz given that it kinda felt like season 2 league but sped up. #BringBackFON