Is the Prometheus system compatible with Wanhao Duplicator i3 Plus?
The Prometheus system is pretty much a Y-coupler and two extruders. So, you need your Wanhao Duplicator i3 Plus to have the connection points for two extruders and the axis, which means you need one free, 4 wire connection slot from a stepper driver. So, let's look what kind of board is in there...



This Melzi Hypbrid is the mainboard the Duplicator uses, similar to a lot of other Melzi derivates (itself as it seems a Sanguino Derivate). The green 4-pin terminal is the extruder. There is only one of these. So it is not useable with Prometheus. You would need to get a mainboard that is able to run dual extruders.