Unlike Ben Heck's famous project, this would not involve a motor.  The key innovation required is a way to back out the glue.  Instead of a trigger, it needs a grip wheel that rotates both ways.  Maybe it could be based on a steering wheel from an RC  transmitter.

The 2nd innovation is a fine point tip.  There would be a fine point & a standard point but this would require 2 guns.  The wheel might be possible in PETG.  The fine point tip requires metal fabrication.  Theoretically, if the glue never heated above 200C, a standard glue tip could be drilled out & there could be a tube soldered on the inside.  Some minimal TIG welding seems to be inevitable.

A stretch goal would be PID temperature control so it could heat up fast.  That could be done with a triac & an existing gun.

Previous experience showed backing out glue causes the stick to stretch.  It would only be backed out slightly to keep it from running out.  Then, the very end of the stick would not be recoverable.  Lions have long dreamed of a way to fuse 2 glue sticks but there was no way to make it strong enough without creating a bulge or misalignment.