Interesting features to be implemented in the core
Media Manager - Upload, Edit (Crop, Scale), Delete, Assign images to
Slideshow Manager - Essential Promotion Tool with transitions and per
slide title,description, link
Caroussel Creator - Essential presentation tool for websites.
Form Creator - Number one functionality for clients (their own forms)
Site Tools - Google Analytics, Homepage Popups (schedule, seasonable,
promotional), Newsletter (auto or manual generated), Topbar slider (for
messages like the privacy one,etc)
Store - If there is one Plugin that clients LOVE is the Woocommerce for
WP, make something similiar and you are good to go
Branded Backed - People like it. Agencies want it.