I've ran into business-relevant slowdowns due to this issue. I live in a statically typed language. Your "at best" is actually very straightforward. Also, sum t

I've ran into business-relevant slowdowns due to this issue. I live in a statically typed language. Your "at best" is actually very straightforward. Also, sum types exist. The problem is that by the time you stream gigabytes of data, if you have done it the wrong way, you now have to add a new API revision for the right format, update your whole ecosystem - if the protocol is even in your control. If you did (or specced) it right from the start, you'd only have to adjust the clients at that point, and it would have been just as easy up until then.