It's like this: 1.0 is our long-term support (LTS) stable release. While 1.0.N is in development the version is 1.0.(N-1). The reason that 1.0.7 exists in our branch is that there will be a 1.0.8. Because 1.0 is the version we support for the upcoming X (X = 5?) years.
1.2.0 is the first release that ships `--gc:arc`. 1.2.2 will be released soon having many arc-related fixes and also other fixes we seemed important enough to backport. Probably there will be no version 1.2.4 because 1.2.0 isn't an LTS release. 1.3.x is the development version that will become 1.4.0. For technical reasons having to do with bootstrapping the x is more frequently updated these days. It's expected that 1.4.0 will ship --gc:arc with the cycle collector. Regarding arc being hard to implement, well, it's still automatic memory management and it works with threading so there is some intrinsic complexity involved. **Everything should be made as simple as possible, but no simpler.**
