The year 1999 (MCMXCIX) was the 35th Anniversary of G.I. Joe as a whole.
Hasbro-Kenner, always tight-lipped about upcoming projects, ended 1998 with no announced plans for more G.I. Joe toys. Early on, there was mention that if the 1998 series performed well, the next year they might put the line into general release. A new G.I. Joe comic book series was also discussed. For a number of reasons, both ideas fell through, and perhaps this was fortuitous: on May 3, 1999, the toy world was taken by storm with the release of Star Wars: Episode I merchandise (much of it produced by Hasbro-Kenner). The new Star Wars movie was in theaters all summer and was re-released just before Christmas, so other toylines had little opportunity to compete. (The 12" Joes were targeted at adults, so their sales did not suffer.)
No toys were produced this year.
No comics were produced this year.
No animation was produced this year.