What does a module author do? If my module uses an API that was changed in 5.x, do I only support 4.2.x, do I only support 5.x or do I write in some hacks to try and check between the two? What if 6.x comes in, say, 6 months and also breaks another API. Now I have 3 hacks or I only support 4.2.x or 6.x.
This is the first major version since the io.js and node.js merger so I'm not that concerned yet but if they continue this pace then I will be very concerned (just like I was concerned when npm was supporting io.js and node.js when they had differences in their APIs; it forces module developers to choose and limit their availability). I would like to see some path of deprecation for node.js APIs that take multiple major versions to get away from unless it's a major security risk.
Edit: just to clarify my worry: I'm not worried yet. But, and this is a big but, ECMAScript doesn't include any standard libraries for interacting with systems, http, etc so node.js has kinda assumed the role of a standard, defacto library for JavaScript when dealing with a system on a level outside of a web browser. So if the breaking API changes are going to occur every year or faster, to me that's like a language's standard libraries changing every year or sooner.
Yes it's kinda not fair as node.js is NOT a set of standard JavaScript libraries but that's the role it's essentially been given due to the lack of one in ECMAScript.