people's views on whether or not it's a safe and viable way to operate an aircraft.
Clearly outside CAS you may not be able to receive a radar service, and even if you can, there may be aircraft the radar cannot see - gliders.
Some will tell you that the evidence suggests from the point of view of collision with other traffic it is safer to fly IFR (IMC) outside of CAS than VFR, because the historical record is significantly skewed in favour of IFR. However statistics do not tell the whole story. There are far fewer aircraft operating IFR IMC outside CAS so you would expect the number of collisions to be fewer in the first place. Taking this into account, I have idea whether the risk is greater or less, but the evidence would suggest the risk of any mid air is very small.
For those who would rather not deal in statistics it is worth remembering that there are some aircraft who are not going to be following the rules of the road in IMC. As discussed recently gliders may be in IMC at any height / level and not transponding. There may be other aircraft not transponding as there is no legal requirment to carry a transponder outside CAS. This means that you can neither rely on TAS or flying at the correct height for your heading to avoid other traffic. Moreover there is traffic below the transition level who are probably flying at whatever height they like.
In terms of other risk there is of course clear evidence that single crew IMC ops is a great deal more risky that flying in VMC. The risk is almost certainly proportional to the pilot's level of skill and currency and perhaps also in part to whether or not he has a reliable auto pilot.