Cool! I’m excited you have thought about it, too.
A few notes on those Chinese cutters:
They have small areas, you mentioned that. Most of my laser work is bigger than 12″. Even if it isn’t, its much better not to have to cut your material down to size just to fit it in.
They have TERRIBLE software and controllers. Like, there is really no worse software. Someday soon the Chinese are going to figure out we just want reprap, but not yet. The software generally borders on useless, vastly limiting what you can do and the operating systems you can use to control it.
Some thoughts on technical hurdles
I have never built a laser cutter before, so I wouldn’t be surprised if I was underestimating the difficulties.
The most obvious problem are the mirrors. I think that special mirror mounting printable axis brackets(if you know what I mean, the sliding part) could be designed or maybe even attachments to the existing brackets that hold the mirrors in adjustable catches. I think the biggest hurdle here is stability and straightness. I have no idea what kind of tolerances the MPCNC has on the straightness of those pieces.
The second issue would be containment. I dont know if you really want to operate one of those lasers without a case. Supposedly laser glasses make it safe but…I’m not sure. A question better left to someone with more knowledge. Also, cutters usually have air assist and always ventilation. I think both of those would work without a case, although not quite as well. Perhap the existing ventilation boots people have designed could be adapted.
I’d argue that there is a LOT of utility for this idea. If it can be proven theoretically possible, I would hapilly prototype it myself and even design parts in fusion 360 which I am learning. In that case it would help if I could get my hands on the cad files of the rest of the mpcnc parts. But first, I think we need more input from laser specialists.