Pretty sad to see a gamemode get trashed when all it needed was an update. Honestly, they could update TT twice per season and that would be enough to keep it interesting. Yet they somehow have time and the idea pool for the new SR map changes, as well as the new dragon changes, but nothing for TT? So much wasted potential.
Here's how you fix TT in my opinion:
Shorten death timers: No one wants to die at 20 minutes and wait nearly a minute to be able to play the game again.
Rework altars: Despite having decent buffs, the altars don't really do much. Maybe even, instead of making it a game mode where you kill the Nexus, you could have an altar where each Nexus is now, and make it so the objective is to control all 4 altars to win. At least it would be more unique. Think about it. Even if the enemy team is on your base's altar, someone could sneak around and grab one of the altars in the jungle before they control all 4. I personally think it would be a lot more interesting, but even if they just gave the current 2 different buffs, or even scaling buffs, that would be fine.
Change jungle/open up map/rework vision (let us upgrade Oracle): essentially there are 15-20 champs that are any good on the map, and about 50 who are almost impossible to win on. Kayn, Rek-sai, and Fid all have an unimaginable advantage over almost all others because they can go over the thick walls that no one else can. I'd say make the walls thinner, or add a path that leads between the middle of the two top lane bushes. You could even add more camps because the camps currently die extremely fast and don't really do anything. Maybe you could take the scrapped SR idea of smiting a specific camp to get a specific buff (smiting wraiths gives you a spirit that wanders your jg and let's you know when someone is in there, something like that). Also, vision is so good awful, it's not even funny. The easiest way to keep it unique and stick to your guns, as you so obviously do, is to let players upgrade the Oracle. It could be in a short path, similar to Ashe E. It could last longer. Anything. Champions like Teemo get full rein of the map because no one can stop his shrooms, especially if there isn't a champ on your team that builds duskblade. Either add more items that can spot traps, give us more ward options, or both.
Please, Riot. Even if you don't listen to my ideas specifically, at least try to rework TT. It could make your game so much more interesting and fun, keeping players for longer.
Also, real funny how your world's pass doesn't give tokens for playing TT games. It says matchmade games, Riot.