RISC OS emulated on a PC running windows *or* linux in my humble opinion has the potential to *damage* the native RISC OS market. I've said this regarding VA several times - and the same thing applies to RISC OS emulation under Linux.
The *only* differences between the two IMHO are (i). The Linux option does *not* put you at the mercy of Microsoft (ii). Linux as an OS is arguably more stable and less prone to "security" issues than Windows and (iii). The cohort of users likely to use ROS on Linux emulation are likely to be the sort of people who'd have stuck with RISC OS rather than used RISC OS emulated on Windows - but who would happily accept RISC OS running on a Linux based emulator if that were available.
In short I believe the *larger* damage was done by VA - and that some loss to Linux will occur from this new development - but not likely involve as many people, unfortunately it may well be those who are more technically capable and who are therefore more likely to make meaningful contributions to our platform - their loss I feel would be regrettable.
Whether all of this amounts to "another nail in the coffin" or a potential for broadening RISC OS availability to other users outside the traditional market remains to be seen.