I get it now. You want a serial to parallel converter with darlington drivers to handle LEDs and you want it to be expandable. You're right in saying that the 16F628A could handle lots of LEDs with this technique. However, you should be aware that though you are saving on the pins at the PIC, you are not lowering the burden on its coding. It will keep updating the LEDS at a regular rate to let you have the moving patterns you wish for.

The commands could help you are SHIFTOUT or maybe I2C_READ depending on which is relevant to the chips you want to use and how 'low cost' you want to design.