You /could/ do it, but it would mean that you needed to write to the PCF8574 CONSTANTLY and the Arduino wouldn't have time to do much more else.
You need something like this: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface : ID 1411 : $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits
The chip on the board is actually a LED-driver, but the clever part is that it's PWM-frequency can be set, so it emulates a "servo"-signal (what your ESC needs) and you can control the duty cycle by writing to the registers of it.
// Per.