Hi Aivar,
this feature does not exist yet.
However, transforming the model into a more readable format is not a big thing. For example, we have an SCXML Code Generator. It is still XML format, but way more readable than our internal XMI format.
Also a sismic generator would be possible. The main problem is, that you can't use such a format for diff and merge, because it only contains the state machine, but not the statechart. All the things that are stored in the notation model
like layout, bounds, colors, fonts, sizes, and the like would be lost when working on such a model.
Best regards,
Andreas