Google's pending algorithm change doesn't require sites to use responsive design. They only want websites to be mobile-friendly. There are other ways to do that, like dynamically serving different content to mobile users or redirecting them to dedicated mobile URLs.
While this is a significant update, I tend to think the biggest impact will be on websites operated by smaller companies and individuals. The websites of most big companies dealt with this issue a long time ago and many intermediate-sized companies have enough ranking power to mitigate much of the effect of this change. So I think you're most likely to see the bulk of the ranking changes on the second, third, and fourth pages of the SERPs.
Whatever Google or Bing do in this regard shouldn't be what drives you to make your site mobile-friendly. You should do it because mobile users are a large and growing share of web users. E-commerce sites are seeing 30% or higher usage from mobile devices. The low conversion rates on mobile suggests that they're often shopping on their smartphones, but waiting to get back home or to the office to actually buy, but that's still an enormous audience. Even purely informational sites generally have at least 5-10% on mobile - using tablets, if not smartphones. One way or another, if you don't accommodate mobile users, you're throwing away traffic.