Hey, MIke! Thanks for your comments. I pretty much agree with everything you said but do feel compelled to mention that Ryan’s MPCNC platform was originally designed to carry a spindle… and that the addition of lasers, needle cutters, drag-knives, pens/markers, etc. only serve to show its versatility. If Ryan’s original intent was to simply design a laser engraver… yes, it’s overkill.
I like your cantilevered laser engraver design… I’d not seen it or the ModelFlying forum. I have, however, built a couple of Edward Chew’s TimSav foamboard cutter systems… which greatly resembles your machine (and, apparently, that ripped-off Chinese design 
) and carries a needle cutter, originally developed to cut RC plane parts out of foamboard.
When we were doing all the testing during this thread, I had a “stock” MPCNC, running Marlin, that I had set up as a laser engraver… using the M106/M107 fan control gcodes. And, yes, we quickly uncovered the fact that Marlin wasn’t really designed with a laser in mind. While I was getting a reasonably good-looking raster engrave… others were not. Ultimately, we discovered that relatively “innocent” changes in the fan control section of later versions of the Marlin firmware seriously impacted its use for controlling lasers. A work-around was found and soon everyone started getting reasonably good Garfield engravings. But, yes… it is still “lacking”, especially with the stop and go action with power changes and not ramping the power as the laser speed adjusts to enter and exit a corner or boundary.
Fast forward to now… I’ve joined the Lightburn and GRBL crowd. Not disparaging Marlin’s use with MPCNC… but since much of what I do nowadays is lasering and pen-plotting, I’ve found GRBL’s “laser mode” to be far better suited to my need. Several threads in this forum (here, here, and here) show laser engravings far superior to what I was able to achieve with the Marlin-based testing we did in this thread.
And, now, inspired by @geodave’s Rolling Plotter build, I’m currently testing and adapting a version of it as a “rolling gantry” machine. It not all that dissimilar to your machine in that… it uses “tractors” where your machine’s feet are, uses the long axis almost verbatim, and essentially turns your cantilevered axis 90*, to become the Z-axis.
As mentioned, I’ve also joined the Lightburn camp and can’t begin to say enough good things about it, when it comes to laser engraving. One fellow in particular, @Bulldog on the Lightburn forum, has been doing incredible engravings on wood, ceramic tile, children’s scratch pads, etc… all with just a 2.5 watt laser. It’s been great fun applying his tricks and techniques to my own engravings.
Again, I like your work… and thanks for sharing! I look forward to seeing more from you… 
– David