Take a time machine back to 1994. Which file formats from then are still in use today? Precious few. Many of the ones that did exist were still in their infancy, and had a very uncertain future.

Rather than trying to predict what will be supported in 20 years, I'm going to suggest converting file formats as the future itself dictates. When doing the conversion, try to stick to as similar a file format as possible. For example: that 1994 Postscript file would have been converted into a PDF file. Always keep the files in the original file format, so that you don't progressively lose formatting or content as time goes on. Also keep as many intermediate formats as you feel comfortable with, since the original format will eventually lose favour and different conversion paths will have more or less desirable results.