Quesabesde published an interview with Hiroshi Kawahara, Operations Manager at Fujifilm. The answer to the last question hints at future high-end cameras that will follow the X100:
"Q: With the FinePix X100 Fujifilm comes back into the world of professional digital photography. Is the following step to recover SLR cameras too or is that road definitely closed?
A: I'm happy to hear people commenting that Fujifilm came back to the professional market. The FinePix X100 is the starting point of the high-end cameras to follow in future, and although I can not tell you anything specific at this stage, please look forward to new Fujifilm cameras in the future."