We are working to improve the Export functionality. In the next major release it will be possible to export the entire Timeline area. But the number of the tasks that can be exported fully depends on the browser and machine that you have. Some browsers cannot handle large amount of data. That's why I would recommend you test and see what is the limit.
Regards,
Hristo Valyavicharski
Telerik
Regards,
Hristo Valyavicharski
Telerik