You know, after watching the Xayah spotlight, I'm remind of another marksman
A marskman that currently has no identity as a generalist or a specialist whatsoever.
http://orig13.deviantart.net/925b/f/2016/147/b/3/tristana_by_vegacolors-da40hrc.jpg
When is Riot going to look at Tristana again? Let's look at her abilities and compare them to other marksmen.

Out of all of these marksmen, is there anything that Tristana can claim at being better at than any other?
Range? Caitlyn, Ezreal, Jinx, Varus, Kog'Maw, and Twitch beat her there and Caitlyn beats her until LEVEL 16 without needing it to take up a passive slot or be on a cooldown with an ability.
Steroids? Draven, Jinx, Kog'Maw, Twitch, Vayne, Ashe, Caitlyn and Xayah beat her on that. Tristana's steroid is also the only one that takes up an ability slot and gives nothing else but attack speed, everyone else has a steroid with additional effects, like Kog'Maw getting an active with an Armor/MR shred or comes passively like Jinx's Q.
Safety?
Caitlyn (Again) Ezreal, Lucian, and Vayne can all play just as or more safe than Tristana while also still being able to effect a fight, remember that Tristana literally cannot do anything to anyone without being in auto attack range of them and Tristana's E requires her to stay on a single target for a while to get the max damage from it which is not safe for a marksman with the game having so many champions with multiple gapclosers or ridiculously long ones (
being yet another example of Riot refusing to stop piling on the mobility creep). Tristana can make herself safe with her W and ult but if she does then she's then out of range to do anything in return to her enemy without them jumping on her again.
Mobility? Caitlyn (AGAIN) Ezreal, Kalista, Lucian, Quinn, Vayne, and Sivir all have better mobility tools. You may say "But Tristana's dash has 900 range, more than any of them. More range on the dash of a marskman doesn't mean anything when forcing a marksman to use that maximum distance results in them no longer being able to influence a fight, especially when its on a longer cooldown than any of the other dashes.
Keep in mind also the disparity between Tristana's and Caitlyn's. Caitlyn's is intuitive, it makes her go one direction, launches a skillshot that can slow in the opposite direction that can stop a pursuer, deals damage and triggers her passive on whoever she hit giving her an enhanced auto for a chunk of damage. Tristana's requires her, a squishy marksman, to jump ONTO a dangerous enemy in order to proc the damage and slow, ostensibly its meant to encourage her to go all in on someone but she's not Lucian, she doesn't have a lot of upfront burst damage, her E requires time to stack to get the damage off and if that person backs off while others move in then she just lost her big damage source.
Burst? Lucian, CAITLYN, Jhin, Varus, Vayne, Corki, and Graves all have upfront fire and forget burst damage that doesn't require you to hit someone four times to deal it.
Pushing power? Sivir, Xayah, Graves and Jinx do it better and don't need to use an ability that's also their main damage tool for enemy champs and their tool for taking turrets to do it. Tristana also can't control her pushing power thanks to her E passive so she can't reliably freeze a wave, so if the enemy laners decide to just passively farm then the wave will push towards their side and their jungler can come for a gank.
Turret taking? At some point all marksmen take turrets fast but Jinx beats her by a long run at all stages of the game. At every stage of the game Jinx can take a turret faster than Tristana and as I said before, without needing to use her main enemy damaging ability to do it. Freaking ZIGGS was doing a better job than her when people were taking him bot lane.
CC? Ashe, Caitlyn (AGAIN) Jhin, Jinx, Varus, and Quinn have her beat there since Tristana's W requires her to jump ON her enemy to use it leaving her with only her ult as her big CC source but it also pushes enemies out of her range, meaning she can't counter an enemy after using it unlike Varus who can use it as an opportunity to treat them like a sitting duck and shoot them a bunch.
Tankiness? Graves is the only marksman that's really tanky but you'd think that Tristana, who's encouraged to go all in on someone would at least be more durable to make it less of a death wish than it is but she isn't, Miss Fortune has better base defenses than Tristana.
Generalist? Lucian has been the generalist marksman forever, the one that's used (When he's not nerfed into unviability) as the marksman you pick into any matchup, but even still we have again... Caitlyn and to some extent Jinx as good generalist picks as well.
So wtf is Tristana supposed to be picked for? There's nothing she's outstanding at and many of what are supposed to be her best strengths are outclassed by other marksmen who also get other benefits on top of them. She desperately needs a second look at to refine her kit so it has some kind of focus on something that she can do well and be picked for over other marksmen. She should at LEAST not be so outclassed by Caitlyn, buff her passive so she gets more range than Caitlyn before level 16 at least, most games don't even go on that long.
Maybe make it so if she ults someone with her E on them then once that target reaches the max knockback distance then the bomb instantly explodes for max damage, thus giving her some kind of instant burst damage and a way to influence a fight outside of her auto attack range. Maybe remove her E passive and instead make it part of her Q active where it acts a bit like Kayle's E splash damage. Maybe make it so her passive also gives her additional crit chance per level on top of the range? Or maybe have it so her range scales with her crit chance? Maybe give her back her base attack speed so it isn't so trash without her Q up. Do SOMETHING with her.