Thanks for the suggestion. Actually we have tried to use that approach already, but with the current HTML rendering we are using it is not possible to be implemented. We found that this really awesome feature for -moz and -webkit browsers is useful for some specific cases in small projects, but it could not work for the Spliiter case. We hope that in a future releases Firefox and Webkit browsers will support more useful text orientation CSS rule, so we would be able to use it.
All the best,
the Telerik team