To add to that: there are several major stablecoins on Ethereum: USDT, which is backed by BitFinex and has $12 billion in circulation, USDC from Coinbase/Circle with $3 billion in circulation, GUSD, from Gemini, BUSD from Binance with $700M in circulation, and DAI, which is decentralized and has $1 billion in circulation.
These are all ERC20 tokens so easy to integrate into Radicle, and offer a way to allow developers to get paid peer-to-peer while completely avoiding the price volatility of typical cryptocurrencies.
There are so many issues with email that I'm not even sure where to start, and they've been repeated many times in previous HN threads anyway. Suffice to say that clearly it doesn't work for a lot of people, because otherwise we'd all be using it.
I know about git-send-email. But you still need some kind of website for project info and code (unless you only wanna give out your code on request via email) and a patch/bug tracker if you want your project to be approachable. Larger projects and business users might also want CI.