A year and a half ago, I made
a suggestion to include spoiler tags as a BBCode ([spoiler][/spoiler] or, a shorter version, [sp][/sp]).
It's a small inclusion that has the potentially to drastically improve the User Experience. It gives posters the option to hide large images and wall-of-text style posts in manageable blocks, or to hide disproportionately large images/a number of images inside of an expandable block. This also will give it the opportunity to hide actual spoilers.
Lazy loading could also be incorporated to help users on slower connections load the page before the content in spoiler tags, which could help speed up posts which use it. However, lazy loading is hardly a core feature, but may be something that could either be a plugin, or incorporated into core after a stable platform has been created.
Examples:
http://jayisgames.com/spoilerinfo.phphttp://www.reddit.com/r/asoiaf/comments/i2mg6/attention_we_now_have_a_new_spoilertagging_system/ (Text Only example)
http://www.goodreads.com/topic/show/485694-spoiler-policyhttp://forums.animesuki.com/misc.php?do=bbcode#spoiler