Is there technology today that eliminates the latency in a video conference so that two people can sing together or something despite the distance between them?

Yes! You might want to look into variable bit rate streaming (VBR), Mpeg Dash or dynamic adaptive streaming.

Though these are different, they all basically split each file into smaller sections which allow compatibility across multiple platforms with significantly less latency.

For instance, if the end user is using a smartphone, the stream can be adjusted to a smaller size to maximize quality vs speed giving the end user the best possible quality per available bandwidth.