If you limit the feat such that "you cannot have more sneak attack dice than BAB", then it's not a bad feat. But I'd never give up a series of 10-11 feats for full sneak attack as a fighter -- I'd be useless against anything that's not living, that's too far away, that the dm rules keeps its vital bits out of reach (halfling with a stick vs. Tarrasque?), and anything that's giving its undivided attention to you.
The last one is the worst: The nice thing about the bigger HD, full plate armor and tower shield using fighter is that it means you can get a creature's undivided attention while the full-class rogue of many talents gets into position for a bunch of brutal sneak attacks. (If you can't get the monsters' attention before the rogue gets into position, the rogue may not make it into position, you know?)
Vice versa is definitely not the case. Take away a rogue's sneak attack and give them 10 bonus feats and you'll be very scared because they'll likely only take half of their sneak attack and spend the rest getting things like "Weapon Finesse, Exotic Weapon: Spiked Chain, Dodge, Mobility, Spring Attack" or "Martial Weapon Proficiency, Point-Blank Shot, Precise Shot, Rapid Shot, Improved Critical: Longbow" or something like that.
Don't they have like a "+3d6 sneak attack" feat in the generic classes section of UA?
Cheers,
::Kaze