"How likely is it that anybody is going to be able to volunteer to represent an organisation they're not part of? Why did ROOL agree to go in the first place?"
Maybe at the time they agreed, they could attend? And perhaps now something more important (this RISC OS thing being a spare-time, and hence by necessity low-priority, activity for many) has come up, meaning that they can't attend any more?
I'd imagine that it would be possible, in theory, for one of the developers working on RISC OS 5 to talk about the project. Whether anyone will want to is a matter for them.
And in the end, if you don't ask, you don't get...