There seems to be an upgrade path for cutting steel with a slower spindle and extra steel plates for added stiffness. There are other DIY CNCs that are designed for steel and use concrete for stiffness which are probably more appropriate - but they do cost more so it really depends on your needs.

What I think will really change things are the 3-in-1 fiber laser sources that can be used for welding, cutting, and cleaning. Building a CNC gantry that can use the cutter means large pieces can be cut from stock plate, assembled like a 3D puzzle, and very quickly welded together. While much more expensive than a Milo it is be a totally different category for capability. Plus a handheld laser welding, cutting, cleaning are very useful tools in their own right. I think laser welding is soaking up most of the supply at the moment but I also think it's just a matter of time before people figure out how to hook up the cutter to a CNC gantry like many already do with hand held plasma torches.