Things that would make TFT more Enjoyable than it already is....
To start with, TFT is an enjoyable game mode, more chill than regular league. I'm not here to suggest competitive changes or complain about bugs (I mean I could but that's not my current point).
TFT and League are not the same thing, and I think Riot needs to firmly decide what they would rather do. Tie League and TFT together more, or turn them into their own separate entities.
Not getting XP for playing TFT is frustrating, but it's understandable Riot doesn't want your league level to carry less meaning.
So why don't we give TFT it's own level structure? It wouldn't be anymore complicated than the current league XP structure. Every account could have two levels, one specifically for league modes and one specifically for TFT. By gaining TFT experience, you could unlock TFT specific capsules that could contain Skins, Little Legends, Arenas, or Loading Animations.
To Explain what I mean with a few of those.... Skins for TFT: You know what's cooler than getting a Level 3 Darius in TFT? Getting a level 3 God-King Darius. The ability to re-skin the in-game champions in TFT would be great. Battlecast Cho'gath would be incredible. I personally would love Firecracker Sejuani, or Lunar Eclipse Leona. It wouldn't affect their stats of course, but I feel like this is an inevitable step Riot should make.
Little Legends: It would take the sting out of the current cost and randomness of purchasing little legends. The chances of a LL out of a TFT Capsule shouldn't be high, but a 10-15% chance to get a LL would be great.
Arenas: Self Explanatory, right now it's a little tiresome seeing everyone having the same two arenas.
Loading Animations: Instead of coming through a portal to enter an opponents stage in TFT, how much cooler would it be to have a multitude of "Splashy Entrances". It'd be mighty neat to appear at the base of a bolt of lightning instead of popping out of a portal.
Overall, I think these things would be great additions to TFT. Even if there is no capsule system, I do think Champion skins in TFT should be a thing. Perhaps if it's a skin you own on the champion in league, it should be available for your champion in TFT. It could be set prior to game.