Yeah, while this is theoretically possible it's unmanageable in practice (the "washing line" protocol allows you to send a UNIX pipe file descriptor to another process over a socket).
I suspect the nearest thing that made it into production was OLE.
This is the construct used to program the spreadsheet's reactive behavior, after all. You could think of users creating spreadsheet formulas as declaring a pipeline at runtime between two datasets, the origin range and the target range.
What is missing is a way to create "spreadsheet functions" among different applications. Online computational notebooks a la Jupyter are almost there, but they still need to share the same runtime kernel to transfer data between different books.
A combination of notebooks and web hooks should do the trick, methinks, but it needs someone to assemble this brittle system into a robust product.