Thread hiding, image expansion
Those are purely display issues, and should be handled on the client-side. Either write a bunch of JavaScript and throw it in the Karenhegivesashit header, or leave it to the end-user (ala firefox extensions/greasemonkey scripts).
make some threads immortal, support many filetypes, extracts album art from MP3s, preserves filenames, and has a player
Aside from the player (I fucking hate bullshit built-in players -- if I want to listen/watch/wank I'll download the file myself and play it with native software thanks), these are somewhat more viable reasons. Again, there's nothing really ground-breaking here -- you could easily hack this shit in to existing software in 50 lines or less.
"sage" and "noko" should lose their nondescript names and be checkboxes
Again, easily done in under 50 lines.
While I'm not going to argue that there are benefits to writing your own software from scratch (makes your penis feel bigger, etc), the fact stands that hacking in such simple features isn't a valid reason to do so.