not just hypothetical — i've started working on this, and do plan to finish
Regenerate/refresh cover image of bookmarks
OCR every image and allow full-text search on images that have been seen
allow sorting channels by:
built-in support for grouping channels from a single user by prefixes?
better previews for twitter links
(from either twitter or nitter api, depending on which one's easier)
shows both when blocks were first added and when they were connected to a channel by default
tree-style tabs, as a sidebar, to help structure going down rabbit holes
keeps history of every time you viewed a block/channel, and the path that you took to get there
allows filtering blocks by when they were last seen (only new, only already seen, only seen more than a year ago, etc)
allows "expanding"/flattening superchannels, up to an arbitrary depth, so you can use superchannels to make custom feeds
