Well initally there was RO 4.xx in 26 bit by ROL and then 5.xx in 32 bit by CTL. Things were nice and clean those days (well while we had Acorn around even cleaner...)
And then ROL decided to name their version 6.xx to make the version numbers less clean... and just to increase confusion they call it "RISC OS Select xiy" with different x's and y's and even named one version "RISC OS Adjust" - perhaps some future version will pick up on the third mouse button....
Since both RO threads are "RISC OS" versions and RO5 is not intended to be IYONIX only and "RISC OS Open" is already there those names are no option.
Perhaps the open source RO5.x and whatever follows should be called "RISC OS Future" (not "RISC OS Ultimate" since Microsoft might claim a copyright for that name as OS name) or the like