Using a client app to read other people's posts is an impoverished experience compared to the web pages LJ generates. Since syncitems is (intentionally) crippled, the only mechanism (besides screen-scraping) to read posts is the news feeds. These include only the standardized elements for RSS 2.0 and Atom, so there's no way that even an LJ-savvy client app can display the missing metadata. I've been reading LJ for a while using a news reader (Safari RSS, which I work on) and while there are benefits (offline access, searchability, less load on LJ's servers) I really miss the extra info.
What can I do to help move this forward? Unfortunately I can't offer to write the code, since I don't know Perl and don't have the mental bandwidth to master another sourcebase the size of LiveJournal's. But I suspect the job of coding these additions would be straightforward; the harder part may be reaching agreement on what they should be, and I'll gladly facilitate that.
Here's what I think is needed:
These will require defining a custom namespace, I think, since they're not part of Atom or any version of RSS. Some might be covered by the Dublin Core, which I don't know too much about.
• Per-post images, since each post can have a different userpic. This would be functionally identical to the top-level RSS <image> element, just the tag name/namespace would have to be different for the feed to remain valid.
• Per-post mood. Something like <lj:mood>grumpy</lj:mood>
• Per-post music. Something like <lj:music>Music For Airports</lj:music>. Care will have to be taken to escape the contents appropriately since people do put HTML markup in here (like links to the iTunes music store.)
• Number of comments. The RSS feed already contains the link to the comments, but it's also useful for the client to show how many comments there already are (and to be able to notify the user if comments are added to some post s/he's interested in.)
Does anyone with LJ coding skills want to help pursue this?