[wp-hackers] Tracking changes for posts

[Wordpress Developer]

I'm developing for a platform that pushes out posts to other systems on
publish. I'd like to be able to inform these systems when there is an update
to the original item, be it a new excerpt, title, or whatever.

In an ideal world I'd be able to do this through something like pubsubhubbub
but the Wordpress plugin is hooked to a publish event vs. the
transition_post_status hook, which is what I'm looking to use.

So right now I'm scoping out creating a DB table that will track posts
changes such that I can create an RSS feed of items those outside systems
should update.

Does anyone have some advice as to the best way to go about tracking changes
for posts? I imagine I look for $post->post_type == "revision" -- but then
what? Is there an elegant way to narrow down to the morsels of info that got
updated?