The chances of it getting through within the next few years, is 100%, in my opinion. There will be numerous opportunities to fix this particular problem, along with all the other items getting targeted when it comes to tax & regulation reform. It has wide bi-partisan support, and the tech industry is the largest lobbyist force on earth now, as such it'll be a matter of how soon rather than if.
One counter point... think about who is lobbying for changes. If it's primarily founders/executives at startups, know they do not stand to gain from removing these golden handcuffs. This bill will make turnover higher and hiring more expensive.
It's a double-edged sword. It also means that it will be easier to hire people away from the start-ups. Google/Facebook/Amazon, even Oracle, must be getting a lot of "nos" from start-up people who'd be interested, but are going to hold out for a year or two more (and who aren't quite valuable enough to buy out).
