The total sum of complexity to learn/use would be about the same (and Python would get multi instruction anon funs.)
Plus, it still doesn't solve the piping issue. constructing a command as a sequence of operations like:
p.foo() | len(p) | p + 1 | str(p)
is much easier to follow (and modify) than
str(len(p.foo()) + 1)
this is not a big deal for programming languages because we use variables, functions and other ways of structuring our code, but those don't map well to oneliners.
python -c 'import sys; a = int(sys.stdin.readline())) ; print(range(a))'
EDIT: Not that I'm saying piep is useless; far from it, it seems very interesting. I'm saying that optional {}s wouldn't solve the problem that piep is trying to solve.Another example: map {} is better than having to learn weird single instruction variants like list comprehensions. And so on.
In this case, it is easy to have a shell alias that loads a module and executes its parameter in any other language. Then you have any piep functionality not already built in. Ergo, no need for extra things to learn, in those languages.