El hilo de los AD Carry

IMO Ashe as a whole is in a pretty good spot. She sees decent play and maintains a decent win rate across all elos while also being a niche pick in the competitive environment. Her kit has clear strengths and weaknesses and offers Ashe players many opportunities for extreme high moments.

What is NOT in a good spot is Focus, Ashe's passive. As far as the majority of Ashe players are concerned it provides one singular moment of play and power to Ashe over the duration of the entire game. This is during the level one team fight/lane engagement. For the rest of the game the Ashe player tends not to notice or care about Focus and if she does notice it she feels as though she has no way to be proactive and take advantage of the power it is providing. Not cool.

So what to do? CHANGE IT OF COURSE! Here's something CertainlyT and I just put into testing:

Ashe gains 3/6/9/12/15/18 stacks of Focus for every 3 seconds spent not attacking. At 100 stacks her next attack is guaranteed to crit. Her Focus stacks will then reset to her current Crit Chance.

Note - Attacking no longer causes Ashe to lose focus.

The goal here isn't to do a massive Focus overhaul but instead make a lighter change that turns Focus into a binary mechanic that you can plan and play around in lane. If you have full stacks of Focus you get a free crit on your next attack. If you have 90 stacks of Focus then go hide in a bush for 6 seconds, get Focus, and R+W+Crit the enemy Sona.
Ashe gains 3/6/9/12/15/18 stacks of Focus for every 3 seconds spent not attacking.
To clarify, stacks per 3 seconds are a function of Ashe's level. At level 1 she gains 3 stacks per 3 seconds. At level 18 she gains 18 stacks per 3 seconds.

so her focus stacks reset to her current crit chance, that means you have 30% crit chance then focus makes only needs to charge 70 stacks? and do the stacks function as basically 1% crit chance each?
The first part is correct. If you have 30% Crit chance Focus will start stacking at 30 and you will effectively only need to charge 70 stacks.

The second part is wrong. Focus stacks do not give crit chance like they used to. If you have 99 stacks of Focus you get +0% crit. If you have 100 stacks of Focus you get +100% crit.
This is nice, but it still does nothing for her later in the game during teamfights. Ashe's current passive does nothing for her except on her first return to lane. This one is better, but still demands that she stand around doing nothing to get anything out of her passive at all.
Ashe doesn't have to be "standing around doing nothing" to stack Focus. Only autoattacks cause it to stop stacking, using Volley and other spells does not. That said you are right that it is not the best passive out there for the teamfight scenario. I would respond that it really isn't intended to be. She has 600 range, great base AS, R, and perma-slows for teamfights. Focus will however still give her the odd bonus crit in late-game Volley kiting situations.
I don't play Ashe much so I don't know if this matters -- But wouldn't it be better if she gained 1/2/3/4/5/6 stacks per second rather than 3/6/9/12/15/18 per 3 seconds? It would mean that Ashe can slowly charge her passive with smaller delays between attacks, rather than three seconds at a time.

Wouldn't that be better? Even in a teamfight it might actually allow intervals where it can stack?
Oops should have clarified that. It will almost work like you're suggesting.

After 3 seconds of not attacking Ashe's Focus stacks will update every second.

Timeline after not attacking looks like this at level 18:
1 Sec - 0 Stacks
2 Sec - 0 Stacks
3 Sec - 18 Stacks
4 Sec - 24 Stacks
5 Sec - 30 Stacks
6 Sec - 36 Stacks
etc...

If she has 55% Crit it will look like this assuming she starts @ zero stacks.
1 Sec - 0 Stacks
2 Sec - 0 Stacks
3 Sec - 73 Stacks (55 + 18)
4 Sec - 79 Stacks
5 Sec - 85 Stacks
6 Sec - 91 Stacks
7 Sec - 97 Stacks
8 Sec - 100 Stacks, Next attack will Crit and clear Stacks.