The problem with combining a laser with a print head to perform some kind of heat-ahead function is you cannot predict the vector direction the head will be traveling with current hobbyist firmware, like Marlin, without modifying it sufficiently enough to buffer the GCODE so it moves the focal point of the laser to the next vector direction while still extruding in the current vector.
You'd be effectively operating two independent print heads at the same time, otherwise if you're just focusing the laser at the extrusion nozzle, you're just heating already heated plastic, or worse, burning the current layer of plastic behind the traveling printhead.
The problem with combining a laser with a print head to perform some kind of heat-ahead function is you cannot predict the vector direction the head will be traveling with current hobbyist firmware.
That's not a particularly difficult problem, although doing it on a machine with Arduino-sized RAM might be difficult. Large machine tools which interpret Gcode do considerable look-ahead, because they have considerable inertia and have to slow down well ahead of stops and turns.
https://hackaday.com/2017/11/27/entry-level-3d-printer-becom...