Optically isolated measurements re: the voltage signal are an attractive option. The main issue as I see it is that the number of potentially 'hot' components goes up considerably. The transformer, fuse, switch-mode power supply, etc. are all explicitly UL-listed, which should allow me some day to get the whole assembly listed quite easily.
One attractive alternative to the above is the Avago series of precision opto's
. Very linear. But the circuits required to make it all work are extensive, making for a much larger PCB than I would like.
Another option is to simply run the resistors straight into the ADC and then use the ADUM5401
series from Analog to provide power and a safe SPI bus interface. If I had to ditch the transformer, I would prefer this solution for its simplicity even if it means adding yet another 3.3V power supply to the design (one for the Analog, the other for the digital power supply of the MCP3911).