I plan to start a chip design business with minimum resource and aggressive unit price. To address that, I am looking for a royalty-free 8-bit CPU and I wonder if Opencores' 8051 flavours can be used without entering patent litigation for an fpga and then the MCU.
I plan to build the whole architecture around this core by myself.
Since you are prototyping with FPGA, it should not be difficult for you to verify the core quickly. My experience is the designs in OC are usually not optimized. What is your application? Is the core in your data path, or it is just sitting on the side to do some configuration? If your performance requirement is not very high, it may still be a good fit to your project.