Thanks for inquiring Aspose.Slides.
I like to share that Aspose.Slides allows you to generate the PPT presentation slide shapes thumbnail including rectangles, text frames and tables. However, the charts are supported in case of PPTX and at present the support for generating PPTX shape thumbnail is unavailable. However, we are working over merged Aspose.Slide API for PPT and PPTX and the said feature will be implemented for PPTX as well. The merged API is expected to be released by Q1 of 2014. For, PPT shapes thumbnails, please visit this link.