I think that 21 April update will change something in the air. If you have a website with a solid audience, nothing will change of course, you will still have your audience. But this day will shake a bit Serps and websites in general. What changes do you expect?
I believe Google will launch a new mobile crawler (probably with an Android user-agent) that can do a better job of crawling single-page web apps, Android apps, and maybe even Deep Links in iOS apps. The new Mobile-Friendly guidelines that launched last month focus on exposing JS and CSS because Android apps are built in Java, and single-page web apps rely heavily on JavaScript for their fluid, app-like experience.
After few months down the line, Google will come with an update that will say "Okay, if your website isn't responsive, we will flush you out from people searching through desktops as well". MARK MY WORDS!!
We can expect ranking of mobile friendly sites up, not mobile friendly sites down. Lots of rumor after that. I think 21 April is the Judgement Day for all of us.
I think it will more depend on mobile friendly websites: I ready this article: http://mobileoptimization.weebly.com/blog/-why-mobile-optimization-of-a-website-is-crucial-in-the-2015