For the general community, there is a guide linked in the post about how to prepare images for engraving. Haven’t read it, I assume good stuff. Read the comments on Hackaday though, because the guy who made the guide apparently did a few things less than ideal.
For the GlowForge crew, a comment talks about Mr. Beam Jr, and says it uses a fork of Octoprint (web based system) to do greyscale.
Now… I am not sure if they just mean spacing out engraving dots to get a different color, or if they mean dynamic power adjustments to obtain different depth. But at the least, there is something out there which may get you considerably closer to a major feature development with minimal time invested.