Requested feature overview description.
Adding in the previous and next buttons (and their respective hotkeys) while sorting posts.
The buttons i am referring are these <<prev (whatever tags i search) next>>

Why would it be useful?
I, and I assume many, use the prev and next buttons frequently for fast scrolling through new posts, a specific artists posts, and more. Often times I use the hotkeys for it to be even easier.
My one problem though, is that when the posts have been sorted with some kind of order, order:score, order:favcount, etc. These buttons and their hotkeys are no longer available and I'd have to click a post, page back, then click the next one.
Since this is already common place for everything besides sorting, I'd love to see it added for whenever posts are being sorted.

What part(s) of the site page(s) are affected?
Posts, sorting, browsing

This was an intentional choice made by the development team at the time. Due to the cost of fetching arbitrary items from inside a sorted list, it didn't scale to the popularity of the next/previous button usage, and was removed as an option.

If the site ever moved towards an SPA for the posts pages, this becomes a lot more viable, but I wouldn't expect to see it before something like that happens.