funcoperators is pretty neat ! But at this stage of the discussion I would also try to get automatic string casting since the purpose is to assemble a string.
It would be great in the stdlib because switching between os.path.join and str.join is so error-prone, and assembling strings seems like a pretty common task. It's not uncommon to find str.join in arguments against Python.
Monkey patching str in PYTHONTARTUP.py would work, but then that would require users pulling my package to also hack their startup script. Or even worse: we could patch the startup script upon package installation. It seems like it would make redistribution a lot harder than it should.
Another approach would be to add a stringify(delim='\n') method to iterables, it would accept a delimiter argument and would return a string of all items casted to string and separated by the delimiter.
That would be certainly more backward-compatible than supporting an alternate str.join(1, 'b') call.
Meanwhile I've opened a PR on boltons, but, well, it looks a lot like php.net/implode, and I'm not really sure we want that :D