How to Make a Beloved "Featured Game Mode"

From what I can tell from my own enjoyment of game modes like URF, One For All and Ascension, the best kind of game modes are ones that change up the dynamics and mechanics of the game enough to give us something fresh to toy around with and explore the possibilities of all those "What if this champ had really low cooldowns" or "Can a consume a that's consumed a ?" And this is why I feel like game modes such as Nemisis Draft were fun in theorey but kind of failed in practice, because beyond the silly Team Comps, nothing particularly new was added to the game in order to mix things up on the battlefield. This is also why I look forward to Black Market Brawlers because the Brawlers and Black Market add some new possibilities and dynamics to the rift that we League players all crave in order to break from the usual grind every now and again.

 What are your guy's thoughts? Do you agree? Has there ever been a mechanic change that you thought would be super fun as a game mode everyone can enjoy for a little while?