>> I wish I could buy RP2350 with the ARM cores being hard-fused disabled, "cheaper" since no ARM royalties would have to be paid.

Better yet, put 4 RISC-V cores on there!

Not possible without substantial changes. The system bus and SIO are only configured for two active cores; they'd have to be rearchitected to support more. In particular, inter-processor communication would need major changes to support more than two cores - right now, it consists of a single pair of FIFOs between the two active cores.