100Mbps is plenty fast enough to stream 24/192 over ethernet.
The bit about going fibre is of no consequence whatsoever - your LAN speed is dictated by the capabilities of the equipment you're running at home, and if your current router can dish out speeds of 1.0Gbps on the switch side of the router then that's 10x the speed you need to stream 24/192 files.
The fibre part will give you speedier connectivity to the outside world, so the possibility of streaming uncompressed 16/44.1 (uncompressed CD quality) from remote servers (Tidal or Qobuz), and without buffering becomes a reality.