Jazz, those are very nice machines, especially the blue one.

You are right about the benefits, but I was thinking about moving gantry type machines, which are more popular and common among DIY builds. The ones you are showing are moving table type, and no doubt that moving the whole beam up and down, instead of just the spindle, would have a rigidity benefit there, as well as it can be made with more throat (Z to table) clearance also, without losing rigidity. For my moving table type of DIY machine, I also considered this type of solution, but then in the end, abandoned the idea for some reason, probably because it was my first build and was not that confident. Today I'd go for that solution, because for a moving table type of machine, it definitely is a good idea.