1mm nozzles and long leadscrews are generally AliExpress available.
Frame and Z-axis rigidity, vibration damping are going to be complicated, but super stretching an existing 0.4mm CoreXY to, say, 300x300x600mm, isn't that complicated in principle.
The other issue is the heating element. As the nozzle size gets larger, the rate limiting factor is no longer the motion system and whatever adaptive control, but how fast you can melt the plastic.
Most consumer 3d printers can't really take advantage of these large size nozzles, although you could print slowly and it'd still be cool!
Frame and Z-axis rigidity, vibration damping are going to be complicated, but super stretching an existing 0.4mm CoreXY to, say, 300x300x600mm, isn't that complicated in principle.