Actually, for anyone looking for ideas on upgrade paths between Nim versions, here's a writeup of what we're doing: <https://discuss.status.im/t/the-road-to-nim-1-6/2305>
In particular, it involves testing with multiple nim releases, and recognizing that when developing libraries, a library is more useful the more versions of its dependencies that it supports (and tests) - this means that the more generally useful the library, the better it is if it supports older Nim versions - conversely, when developing applications, you want to support only one version of everything and have control over what you upgrade, at when.
