This is a really cool project, but looking closer at the API and issues raised it seems that the features are being over-promised.
- "Do pretty much everything you've used PhantomJS, NightmareJS or Selenium for before".
The main features of those tools plus their ability to handle a large range of edge cases are built up over the years in production use and do not seem to be already in Chromeless. Also, Lambda costs can be a significant point of consideration for professional test automation with large volume.
Nevertheless, there's no turning back as flood gates have been opened and many developers are noticing Chromeless. I believe, with enough dedication from Chromeless maintainers, they may be able to channel the attention and contributions to shape Chromeless to be the main challenger to existing test automation approaches. That will really be a blessing to the open-source community!
The only catch I believe, is it may be easier for those existing tools to be made working in Lambda or implement a similar form of parallelism while still having their mature API, than for Chromeless to catch up to the state of maturity of those tools. But as they say, growth solves almost every problem, so issues like these may be ironed out through collaborative efforts from contributors/maintainers.