Suggestions for Buffs to Marksmen Not Named Vayne
Riot isn't going to nerf Vayne, they want to make her counters stronger to take advantage of her early game. Sounds good. Let's talk about that.
Allow Hawkshot to reveal stealthed units at the point of it landing (seriously, the ability does NOTHING but grant vision, compare it to Kalista's Sentinel and at least give Ashe some bonus utility).
Change The Bloodthirster to be built out of Cutlass and Pickaxe + cost (same final cost and item). If early and mid game carries can rush Cutlass at the same time as Vayne, she won't be so safe and hard to kill early.
Sigh...Okay, dump Essence Flux entirely. Give Mystic Shot an 80% AP ratio so that AP Ez mains won't cry, and give us a new ability. 10/9/8/7/6 second cooldown, fire a projectile in an area of effect like Corki's Phosphorous Bomb, dealing physical damage and slowing enemies inside the sphere, while granting allies inside the area attack speed.
Change Buckshot's cost to be 60 at all ranks, and make Smokescreen's mana cost 80 at all ranks. Graves's early game is just fine but his mid game is horrible because AD mana itemization is horrible. This isn't Season 2, Graves isn't a major threat anymore.
Add a mechanic that reduces the cast time of Piltover Peacemaker to 0.5 seconds if Caitlyn is below 50% max health at the start of the cast. Piltover Peacemaker is a large chunk of her damage but Caitlyn isn't able to use it effectively in trades or ganks because of all the Leonas and Threshs running around.
Corki is rewarded too much for hanging back and punished too hard for engaging. Change his Gatling Gun (which is not the ability he maxes first, so the first rank is very important in lane) to shred 3/3.5/4/4.5/5 armor per half second from 1/2/3/4/5 per half second. (Still caps at 8 stacks). Doesn't affect Corki's current hang back and ult playstyle, but gives him some room to fight back when he's being chain CC'd by tank supports.
The BT change will be enough to help Lucian out.
Give Bullet Time a 50% damage amp when affecting an enemy affected by movement impairing crowd control (snares, stuns, taunts). This will solidify Miss Fortune's position as an AOE team fighting carry and encourage players to pair her with champions like Galio and Amumu (similarly to how people don't need to be told to pick Wukong and Malphite when someone picks Yasuo)
I honestly have nothing here. Twitch is a marksman with long duration stealth. That's just not balance able in my opinion, and I don't want him to be good.

started getting a lil too common for comfort
pacemaker uses up a lot of mana so spamming it isn't a good idea, I think she just needs a slightly higher base attack speed and to reduce by 1 the stacking of her passive at lvl1