After long thinking / discussing / testing out we have decided to try other kind of layout for placing messages in the thread. Like you see it now.
This model still follows the idea of easily recognizable content, but placing username on the left. In the nearest time we plan to work on the avatars add-on which will allow to upload fixed size avatars only. That model will make it possible to place little avatar on the left side as well, and provide couple of strings of additional information from user's profile (like gender, age, registration date etc.) By this there will be not a lot of "empty space" in userinfo row.
I like this model because it follows "mini" concept and it limits placing A LOT of profile info in post, which we always were trying to avoid.
However I must agree if you have a lot of info placed around nickname, there can't be other way than placing userinfo column on the left side. In that case you will need manually edit main_posts_cell template to achieve the better result.
So what we have for now:
1) Username column on the right side is compatible with the current version of miniBB, it brings the content on the first place, however those users who like to recognize post by author first, are not able to do it easily (in that case they will really read from right to left). If such column has avatar, it may make the reading uncomfortable.
2) Username column on top of post is compatible with the current version of miniBB, it still allows to recognize post's content amongst usernames, and it is suitable for the users who pay attention at username before reading; that way they are reading from top to left to right. With this model also there is a big opportunity: each message takes its own table, and that's why the page loads up gradually. On slow connections you don't need to wait until the whole HTML will be loaded up. However this layout limits the using of additional info near user's nickname; to avoid a lot of empty space and unpleasant look of the page, you must care about small size avatars and limit the user's information provided in post.
3) Username column on the left makes the reading of content more difficult and not really natural; however it brings the delight to users who care about usernames and userinfo before reading the post. Such layout also allows to place a lot of userinfo near a nickname. In result it allows to create a shitty look for those boards where near user's nickname there is provided avatar, gender, registration date, custom rank, location, web site, number of posts done etc.
We are on the way of choosing between 1 and 2 :-)