If the PSU manufacturer has a tool that's able to display total power draw, then it should be possible. Though Seasonic PSUs are not supported and I'm not sure if they offer such features either.
Yes, that makes sense. I'll think about such value, but I think it might confuse some users since it will not be a true total power draw, since there is a lot of other devices which don't report power consumed and it also strongly depends on the configuration.