How difficult would it be to increase the build plate size of a 0.2R1 from 120 to something larger like 200mm? I would be OK keeping the 120mm Z-axis print height
You're going to be limited by the size of the extrusions. The v0 series uses 1515 extrusions where as all the other series uses 2020. For something like the v2 or trident, stretching Z is usually not a big deal, but stretching x or y past the stock design limits is generally not advisable.
What's driving you to want a bigger V0 vs moving to a trident or v2?
IMO v0s are a good second printer for someone with a larger printer or for someone who tends to print smaller items.
I have a 350mm 2.4 that I built because I wanted an upgrade in function/quality of life over my 200mm i3 clone and because I often ran into walls with the bed size because I tend to print larger items. That said, I still have the need to print smaller things. A large printer takes longer to heat soak than a smaller one, but if you print PLA/PETG this doesn't really matter. A larger printer will also be limited in terms of acceleration, although it is way faster than my old i3 clone was.
If you can find the extrusions and rails then sure go for it. There may be a direct upgrade path to a Salad Fork or Micron (scaled down versions of the bigger Voron printers built with 1515 frames). Also of note, the Tiny-T is a scaled down Trident that uses 2020 frames.
I built a 180x180x250mm Trident as my secondary printer so it could use the Prusa Mini satin PEI. In hindsight, I wish I had made it a little shorter because it is a bit top-heavy at high accelerations. The bed size is perfect for most functional prints I need. Though I still plan to pick up a v0 at some point for the absurdly small footprint of the machine.
Interesting, although this looks like a significantly more expensive option than the deal I have for a V0. It would probably not be much cheaper (if at all) than a full size voron 2.4 or trident.