Here is the source to the information about the impact on ranking, but no details provided on how much will not mobile-friendly sites lose now.
According to google, if your site is not mobile-friendly, it will lose ranking on mobile searches, but desktop searches will not be affected.
Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices.
Will desktop and/or tablet ranking also be affected by this change?
No, this update has no effect on searches from tablets or desktops. It affects searches from mobile devices across all languages and locations.