More of a speculative concept than an actual plan at this point but what do you think about the potential to make a very large bore (e.g. something I could pass say a 3" diameter pipe through) headstock for the Taig lathe? Would that be practical?

I am thinking a simple solid block of aluminum with a section of say 4" steel pipe through it, supported by a bearing at each end. The pipe would project at each end, on the inside end some kind of work-holding arrangement (maybe a series of tapped holes for cap screws although you'd have to be careful about too much shear force on them while turning), at the outside end a groove for a drive belt (maybe with the standard stepped pulley relaying power via an idler shaft so you could vary the rpm).

What would be the concerns one would need to address to make this work? I'm not sure I would actually do it, the idea just came into my head while I was thinking about turning some detail into the end of a 3 foot piece of 2" aluminum pipe, which is so far just a one-off that I might be able to find another way to deal with. But now that the idea has occurred to me it is preying on my mind...