Quote: "I'd imagine that the GCode itself is drawing lines between where the Vertices used to be"
Not sure but I think it allso adds entrys if you change speed or something so I guess if you just connect all G1 Linear Movement entrys you'll end up with more vertices than the original has, but one could work from that onwards.
Quote: "GCode is for all intended purposes just Layered 2D"
The Format itself, yes, but how do the professionals present it on the screen ?
I use MatterControl Lately and it seems they do a cheap version of number 1. from my post above.
Which is, adding cylinder, without even caring about seamless connections between set positions.
Although you don't care about the layers you could do the same and if you add them to one object instead of creating thousands of objects it should be rendering fast enough I guess.