I have been examining this bug (using b2evo 4.0.0 alpha) and observed the following:

1. Adding the style_formats to the backend configuration does included the style_formats part in the TinyMCE init as can be seen by a view source of the html page.

2. Adding the style_formats as part of the hard coded "$init_options[] = " while it does add the style_formats does not allow the drop-down style menu to work.

I do not think this is a problem with the plugin, but with some of the other core files of b2evo that handles the editing window. Perhaps it is the way b2evo hooks the TinyMCE into the editor window?

I hope the developers will take an interest in this bug and try to track it down.

b2evo 4.0.0a does not include TinyMCE 3.3, but 3.2.7.
The feature is just not supported with it.

With TinyMCE 3.3.8 I've added the following to the "Custom TinyMCE init" and it showed up in the Styles dropdown:

,style_formats : [ {title : 'Bold text', inline : 'b'}, {title : 'Red text', inline : 'span', styles : {color : '#ff0000'}}]

So you are right. I looked at the NEW feature list in 4.0.0 as listed on the b2evo site,

"Upgraded to TinyMCE 3.2.7 (@blueyed)"

and did not pay close attention.

So why don't you include the upgraded TinyMCE 3.3.x with version 4.0.0?

I will not contribute directly to b2evo's source code anymore, and the update happened while 3.2.7 was current.

Somebody else would have to do the update.