I installed SMF and WP on same domain, and they share database (only different prefix). Do you think it would be possible that users of SMF when starting new topic have option to post WP article with same content?

The reason for this is we have old forum that is full of valuable information, but now we want to display this information in a form of magazine, running on WP. Ideally, I would setup categories in WP same like forums on smf. Moderators could then visit each interesting topic, select first (or some other) post and press "show as article". Smf would call WP script that creates new article in category that belongs to originating forum. Users that are reading magazine would then see new article, read through it, and there would be also a link to whole topic on smf. Ideally, on WP there would be also information who created initial post and when (typically years ago), and number of replies from SMF database.

I was hoping that there is some mod that allows that, but apparently there is not. Has anyone came up to similar need or maybe solve this way of integration?

No, all the integration does is shares user db to login.

What I did so far, is setup this link using RSS Feeds. It is actually quite powerful.

On SMF I enabled max. length of posts to be sent through feeds. On WordPress I installed plugin that imports data from RSS and publishes new articles based on this data. So in a few clicks I got hundreds of new posts in my WordPress, all linked to topics in my forum, and categorized according to SMF categories. Date of publishing is correct, which I like. Only the author is not set correctly, but this is maybe due to the fact that I'm the only registered member on WordPress so far.

What would be great now is to count SMF replies below wordpress article. Not sure if this is possible, i.e. is there a function that would return number of posts in specific topic, that would work in html (not messing with database reading)?

Are you modifying the mod to work cross platform entirely? Or are you just modifying your own site?

Didn't understand that.

On SMF side, nothing is modified at the moment. I'm using built in RSS feeds functionality. On wordpress side, I found nice plugin "RSS post importer". It offers to enter URL of feeds from SMF, destination category for new articles, and some editable template that I'm using to insert a link (with desired formatting and comments icon) below every created article.

This part was easy, just simple configuration of plugin. For the future, I prefer much more. I disabled comments entirely on WordPress site and want to redirect all interested parties to my SMF. But as far as I understood, there is not much interest for this kind of integration. I will be happy if I modify my site only to get functionality that I want.

Many years ago I was working on one vBulletin CMS+forum platform. They made exactly that by default. You start a forum, later promote each topic to article if you want, and then arrange articles how you want. Or go other way, you design CMS portal, create tons of articles, add widgets etc. and then dedicate boards for comments on articles. You choose for each article if you wish to display comments below article or only a link to forum topic, or maybe first 5 comments below article and the rest is on forum... Unfortunately, they abandoned that philosophy and new versions do not offer anything like that. But I liked that, so I'm gonna try to combine WP+SMF in similar way, step by step.