About mark all items as read before leaving feed:
I look what I can do, I think I will add an option for that (but it can take a while (or not, you will see ;-)), because I am working on other stuffs)

Edit:
About mark all items as read before leaving feed:
In 07.17 I have added an option to mark all items as read before leaving feeds, you can found it, in Options/Items

Edit2:
About "add a divider line in the feed list in the top left section"
I not sure to understood what you want, may be you can share a screenshot. To report bugs, or to request new feature, it is better if you do that on GIT (https://github.com/dauphine-dev/drop-feeds) in the section issue, because on GIT I will get a notification, here I will not (in fact I get one only for the a new comment but not when a old has changed, but some time I take a look just like now)