Frankly ROS Ltd and Castle should just merge. Share the cost of operating system development between them. John Ballance handles hardware, Paul Middleton handles the OS.
Finish RISC OS 4, port features into RISC OS 5. After a couple of years bring the two streams together into RISC OS 6 and tailor three versions for the different hardware, RISC PC era, A9, Iyonix. All three versions have the same core features but are altered to best run on their platforms.
Different hardware, one OS. Don't screw us over guys and run this platform into the ground over petty disputes.