Don't forget that ROL has only 3 sources of income (I think): -
1) RISC OS Select Subscriptions
2) License fee paid from Virtual Acorn for use of RISC OS
3) License fee paid from Advantage 6 for use of RISC OS
If ROOL suddenly release a RO5 ROM image for use with RPCEmu, that could have detrimental effects to the businesses of Virtual Acorn and therefore ROL. I would have thought it would therefore be in ROL's interest to stop such an image being released for the open source emulator.