He would still need something more. His passive will do the same thing as his W did, but only getting so much AS is not enough, since Ashe gets bonus slow, Graves gets a slide movement, and Twitch can go invisible. I was thinking that it should deal true damage to make it more fun.
Not really, his W is already quite a powerful skill. Gaining his W as a passive would give him a super-powerful early game since he can invest heavily into his Q. I imagine his W would gain other effects, but I don't necessarily think true damage would be the correct direction to move him in, I'd look at giving him bonus MS when he attacks a target with his W active as an example of a possible change.
I also hate his ultimate. It deals no damage and only snares a enemy. Since it doesn't stun, nor does it have adequate ultimate length, it should deal 350/500/650 damage to the one hit. It will keep the passive to snare nearby enemies.
Varus's ult does less damage than the only other comparable ult (Ashe's) because Varus has 4 damaging abilities. He gets more reliable ways of laying down similar damage that are less cooldown gated. It also snares rather than stunning because of the AOE potential it has, it's main use is to force the enemy team to split up, kind of like a soft Janna ult.
Why does Varus' ultimate have to be a poke. Ashe gets a long range stun, Graves gets a perma-blast, Ezreal gets a long range beam of damage, even Twitch gains more damage, more range, and bonus damage to those behind the target. I'm sick and tired of not wanting to use Varus' ultimate, unless a nearby enemy wants to run away.
Varus's ult isn't poke in any way shape or form. It's one of the two most powerful engage ultimates out of the pool of ADC ultimates. Ironically you listed a poke ultimate, Ez's ult is mostly used for poking the enemy team down.
It's hard enough for Varus, with his 330 MS. I don't even play Varus often, but I know that is not right.
330 MS makes him tied for the fourth quickest ADC. The only three ADCs with more MS than Varus are Sivir, Quinn and Urgot and they all only have 5 MS more than Varus.
No movement speed whatsoever, yet his Q slows him down.
His Q slows him down because it's one of the longest range abilities any ADC has. Caitlyn's Q completely stops her movement for the animation and is a similar sort of ability.
His W can be useful, but is a waist of a ability, since it only buffs his Q by 100 damage.
In order for 1 stack W do less 100 base damage at rank 5 you have to be attacking a target with under 2000 HP, in order for 3 stack W to do less than 100 damage it's 666 HP.
His E is nice for team fights, but on his own, this can't even be used for a get away.
His E is an interesting ability. It's an area where he may need some small buffs but over all I feel like it's main use on his kit at the moment isn't to get away, but rather to quickly proc his W without having to charge Q.
His passive gives him only 15% bonus AS for killing an opponent. Really?
20% on a creep and 40% on a champ, no idea where you're getting 15% from. 40% AS really isn't that bad as a passive, if he could have access to it more it would be really good, it is over 1000 gold worth of attack speed after all.
His R is only good for team fights and is for some reason, close range.
His ult is meant to be good for teamfights and ganks. It might need a little increase to it's range but it's really not a low range spell. It has around the same range as Ez Q, which is considered as quite a long ranged spell.
His kit is weird, giving little for AD items, and nothing for AA.
His Kit greatly rewards attacking, by attacking he stacks his W onto a target effectively granting him a bonus 26+5% magic damage on every auto assuming you're able to proc the stacks. He also has a 100% ratio on his fully charged arrow, which has a long range and short CD meaning building AD on him really helps out his poke.