multi-tasking for FPGA or PLD

1. I would say, you get something better than multi-tasking: Full parallel execution of all design modules. Only NIOS II soft processors behave as known from other processors, executing tasks sequentially.

2. You can use it as programmable, intelligent uC peripheral, IO-coprocessor, whatever you like. You have to select an appropriate interface, e.g. SPI, I2C, parallel, to exchange data or commands between processor and FPGA and create the interface logic at the FPGA side.