Unladen swallow has never been an official attempt to solve that. It was the initiative of one guy (
http://qinsb.blogspot.fr/2011/03/unladen-swallow-retrospecti...), during an internship, with basically zero support. And so google never even consdered as a serious solution.
Beside, when they took the Go decision, they were still using Python 2.4. It had poor unicode support, bad async io, no multiprocessing pool, aweful packaging and deployment story and the project of a 3.X breaking everything.
It made a lot of sense, business wise. If you have to rewrite your code base, better rewrite it in a language you control (no PSF to fight against), specifically design for your workfload, and fixing all those quirks, plus running faster and eating each memory.
Today's Python unicode support is top notch, asyncio ensure easy networking code, you can use multi-core easily, deployment is pretty much a solved problem and 3.X is running pretty much for 90% of people. You even have a hook to plug in a JIT inside CPython, waiting to be used, and Type hints to facilitate the handling of huge code bases.
Their decision would probably have been different then, although that wouldn't have made Python any easier to speed up. But if a few smart people managed to make it work, by rewritting python in python, no less, I'm sure a dedicated google team would have done great.
They did it for the slug that was JS after all. But they didn't have the luxury to be able to change the language for that. So they pourred millions into it. Not one guy during an internship.
