How "Mobilegeddon" update positively impacts on mobile website? As there any negative impacts of this update on non mobile friendly websites or pages?

Right ,it will not affect desktop search results.If web pages are mobile friendly then they will definitely get advantages in mobile search result from non mobile friendly webpages.But there will not any advantage in desktop search results. 

As we know mobile users are growing rapidly and smart phone users do any search from their mobiles.It will definitely divert desktop traffic towards mobile.In my opinion if websites are not opening proper in mobile then user will irritate and result would low CTR and High bounce rate of non mobile friendly websites.But it will not affect directly desktop ranking of websites.As google clarify in recent updates that responsive websites will get benefited only in mobile and tablets without affecting the desktop SERP.Non mobile friendly websites will loose its benefit in mobile SERP as mobile friendly website will get advantage over non mobile friendly web pages or websites.