As the WordPress platform evolves, Plug-ins get built that solve problems that in my opinion should become core. A good measure of when a capability should become core is when users need to choose between two popular and incompatible plug-ins. Example WP-sticky and EC3 (the great calendar plug in).
Suggestion: the core engine should support the following attributes:
default: none - posts in chronological order
top of day: post shows at top of a day.
top of blog: post always at top of blog
default: none posts display
plug in control: display when called by reguested by plug in.