I can't fault PayPal for releasing their code as open source. It's great. More companies should do it.
But indeed, I don't think it would be a good idea to wholeheartedly adopt their stack. gevent wasn't even a good idea on Python 2, and I suspect the large companies that use it have built up an armor of best practices and workarounds for its glitches, which you won't know about if you start using it.