I have no doubt that it could be balanced. I just hope its prioritized more than past permanent game modes. That's the main concern. Its a different Riot from back then, so hopefully that will be different.
One of the major problems with past game modes (mostly temporary ones) is that there's very little incentive to play beyond novelty, so once that wore off, the modes were practically abandoned. If the game mode drops off after a month, are there plans to add incentivizes to playing the mode beyond novelty? Adding forms of depth/progression, as an example.
This mode will be launching with a rating system (very similar to the one Double Up in TFT uses), which we think should be a meaningful part of supporting longer term sustained engagement. Also expecting we'll do more frequent, responsive balance changes than some modes would do, given while this isn't meant to be as competitive as SR is it's still a more competitive and therefore balance sensitive experience than most of our other game modes