What we do know is that the current rules and training are not working re CFIT .
The fixed wings developed an IMC rating that has massively improved safety . They now don't need to grope along at sub 500ft to get home or to a suitable airport if they get caught out by the weather . IF , and its a big if , the rules and training went the same way then we may see the same improvement . Also if the demand for cheap helicopter autopilots increased dramatically the price would come down dramatically . I certainly don't see a big difference in safety between a properly equipped IFR twin and a single and banging on about an engine failure during the 1% of time you are likely to be flying in cloud is not a properly thought out argument .... There are plenty of other things that will bring a twin down just as quick as a single !!
The cost of training will of course go up , as will the cost of the helicopter but it would at least give people an option . Single engine planes can I believe now fly commercially ifr and twins cross the Atlantic ... So you never know . I just know I have felt a lot safer ifr in say a suitable squirrel or 500 than grovelling low level . ( obviously with a suitably experienced , current instrument rated pilot !!)