One incredibly useful feature would be the ability to see the URL rating's development over time. This is especially useful if you've suffered a rank drop, to be able to see if there's a correlation with a drop in URL rating as well, in order to know if the rank drop's due to a loss of valuable links. It'd be a useful feature that you wouldn't be able to do without once you have it
Having access to historical Domain Rating data - not just Ahrefs Rank - would be extremely helpful for those of us switching from Moz and Domain Authority. Since DA and DR are both on a 100 point scale, it's easier for me to use DR over AR when communicating metrics to non-SEOs in the organization. Thank you!