SEO impact of migrating from http to https based on my experience.
Drop of Rankings
Website Traffic Decline
Possible Change in Domain IP address
Does not guarantee when you will be able to recover from the migration
Wrong .htaccess implementation could cause serious damage to your website
Implement 301 redirect properly or else you can potentially drop your old backlinks and provide poor user experience
Finally, moving to https is like having a new website
It’s the future of all websites
More secure website connection preventing automated website attacks
Google is promoting security
In preparation of HTTP/2 (maybe)
A minor ranking signal
What to Do?
Do the migration now. Or else you will be loosing from the competition. Look what big brands are doing.