I feel that previewing a .PDF would be the easiest to accomplish and largest bang for the user buck. Then, moving over to other vector files are probably the next best bang for the buck. .eps or .svg... these are highly used for most companies that have a brand library. 99% of companies should. (My bet is .ai would be a pain since it's an adobe product)

Brad and Brady, .PNG files are supported now. We still have to add a few others (like .PDF)

Has there been any update to this? At least be able to preview .pdf or .png