Ashe is viable provided that you: kite really well, have exceptional map awareness, can hit 90%+ of your ECA including across the map, can survive mid without dying against a plethora of mostly-better solos (where mid and late game your pacifism turns into control, and control into wins), and that you have a decent supporting cast. She's not quite good enough to be a "primary" carry. She's best suited to a role as Support Carry, IE, she either needs to team up with a Primary Carry or another Support Carry (like Sivir).
Over the past month or so of me deciding to choose Ashe as my main after my long run as Kat, I've proven yet again that a champion that was largely seen as useless and easily countered, with enough skill, can become quite dominant. High/Top Tier is now resembling Mid/Low tier with a varied assortment of players trying out Ashe. We used to never see her, now she's frequently played.
To those thinking she's "lol easy to play easy to master", think again. She's probably the hardest carry to do extremely well with, because she has no escape. Hence, she's almost completely reliant on positioning, kiting, and awareness. Oh, and Plentiful Bounty is useless. One of these days, this ability will be changed, and likely with it Ashe will become an even better champ. So she's one of the few carries that should actually be slated for a buff, rather than a nerf.
She doesn't get much love because the perception since beta has been that she's an easymode champion that falls off after the Mid Elo range. In many cases, these ignorant perceptions are more powerful than reality. While such perceptions should be taken into account, do not overvalue the assumptions of a few. Very few, nay, nobody currently playing the game has a complete understanding of the ins and outs of every champion. It's best that you prove for yourself whether or not something is viable than to go entirely by public opinion on the matter.