Instagram and threads (and parts of the clusterfuck that is facebook) are written in python and seem to have scaled fine.

How much of them? Parts being made in python isn’t the same as your whole backend being written in 90% or nothing but python. But I guess we’ll see.

If a new python release breaks compatibility, Piefed can keep using the old version of python.

Technically yes, though I wonder how long that would last if the next jump is anything like the last. I can already imagine the people bitching about “SeCUriTy” just like many were when people talked about maintaining backwards compatibility or keeping python2 support in the days of the transition to python3.