The latest issue of Famitsu PS2 has, what could be, some very interesting information. In a Q&A with Hori (maker of various peripherals for the PS1/PS2), they stated they had ideas on how rumble functionality could be implemented.
If Sony doesn’t want to do it, why not Hori? The only catch is that it would require [...]
"Rumble functionality possible on PS3?" - 28.10.06