According to Ken :
So my question is, how hard is it to sweat a 2"+ diameter copper pipe?
I've done plenty of 1/2" and 3/4", so I know how easy it is to do that,
but does it become exponentially more difficult to sweat larger
diameters? Is the plumber going to run screaming from our house if we
ask him to do this? I assume he will want to just rip everything out
and re-run PVC, so should we let him do this?

In a job I once worked on, the (master) plumber had to fish a long run
2" copper _through_ the floor joists. Meaning he had to solder
the pipe between each and every joist.

[This was half of a duplex - in "commercial" work, you have to use
copper even for DWV. Here at least... He did quite a bit of
other large-diameter copper too.]

He was using an acetylene torch without oxygen. A small tank
with a hose to the torch.

It didn't take him very long to do 20ish connections.

Not a big deal - to him at least ;-)

You might find it relatively difficult to do yourself with a
standard cheapie propane torch, but if you used MAPP/MPS
cylinder instead, it should be considerably easier. I use MPS
gas myself now, because it's considerably quicker - especially
if I have to solder something outdoors in high winds ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.