As
@mrsclem stated, koi can get get quite large very quickly.
They will outgrow that 200 gallon pond very quickly. They will hardly be able to swim or turn around in such a small space.
I have koi that are longer than my arm with huge girth. If I had to do it all over, I would only have shubunkin and goldfish.
But that's not the biggest problem. Koi produce a huge amount of waste which will task your filtration. Before you know it, you'll be asking why your water is so green. It will be due to nature providing algae to combat the excess nutrients that are a result of fish waste.
I don't like telling you this, but it's a fact.
You'll probably be ok for maybe a couple of seasons, but there will eventually be a tipping point.