Ruby is actually a good comparison: It has the same kind of switchover, ruby 1.8 didn't support unicode while ruby 1.9 and newer does. The changes happened roug

Ruby is actually a good comparison: It has the same kind of switchover, ruby 1.8 didn't support unicode while ruby 1.9 and newer does. The changes happened roughly at the same time as the py2/3 switchover, but happened much much faster. No incompatible syntax changes happened, no semi-automatic translation between 1.8 and 1.9. A lot of libraries worked (and still do) flawlessly on 1.8 and 1.9, many - including rails - offered compatibility relatively early since ruby 1.9 offered significant benefits over 1.8. There were websites and tools listing the compatibility of your favorite gems[1]. So yes, it is definitely possible to make such changes more gradual and effective both by providing the technical means and by assembling sufficient community support. [1] https://github.com/seattlerb/rubygems-isit19 https://github.com/seattlerb/rubygems-isit19