@Gordon The fact that we can start working with Espruino with just a browser is a killer feature IMO.
From the link provided at https://developer.chrome.com/apps/api_index it appears that the easiest migration path could just be to build an Chrome Extension (instead of Chrome App) as described at https://developers.chrome.com/apps/migration. The extension APIs are here to stay I think. But other stuff, like the USB access might need to get migrated to their web equivalents.
Not sure about the native installer.... at least the default use-cases for the Espruino boards should IMO just work directly from the IDE website for easy starters.
For more I would perhaps think about doing plugin for stuff like https://code.visualstudio.com/ or https://atom.io/ where the binary is maintained by the community already and it is a matter of installing a plugin (both could be based on Node.js infrastructure).