It is a reboot that carries over key concepts from the original series, but is not restricted by anything in the original.
Most of the original cast have unfortunately died. Those who are alive may get cameos in different roles.
It will be as close to the original as the remade Battlestar Galactica was to its original.
There was an analysis and proposal for rebooting Babylon 5 made one year ago. The special effects should match up to the Expanse.