Megaman X-treme (hopefully a *new* X game) is scheduled to be released October 2000! I don't have any information on it, though. I'm hoping it's not just X1 or something on the Gameboy.
I might have some more information soon!
Megaman X-Treme looks like kind of a mix of X1 through 3. IGN.com says it has “new allies and enemies”. Check it out here