Beyond Semiconductor owns all including commercial rights to the OpenRISC architecture. Furthermore, the BA2 processors are not based on OpenRISC architecture but on much more efficient architecture proprietary to Beyond Semiconductor.
The beauty about royalty is you will only end up paying significantly for successful chips ie ones you make a lot of and presumably make some revenue from. Paying an upfront fee means you take all the risk and costs upfront and this might force the vendor to make the fee so low to attract customers that it is not viable
The ARM royalty is usually calculated by the foundary such as TSMC. They know which devices have it and how many wafers have been run, so the accounting isn't that hard. Of course, no royalty is easier. It will be interesting to see how much of the pie Beyond can get.