Will this will make people less likely to use Python in future for some projects? I'm no developer or manager but I figure there'd be a thought in the back of my head thinking "what if we need to rewrite this all again for the next major release"
At a certain point this sort of compatibility/forward motion of a codebase through big language revisions is something that has to be designed as part of the language in either being able to break it down into small enough chunks to chew through in pieces (updating a submodule with the updated language without affecting anything else), completely transparent to the code being run through it (this happens for compilers for C for different standards), or to have a version to version automated rewriting mechanism that is so reliable the outcome of the automated tool is not in question (tools like Go's gofmt). Python in my opinion only has partial solutions to all of those answers so it turns into a lot of hand work.
So while there are other languages that may do other things better there are still a class of programs that are very effective to write in Python, and that's plenty enough reason to keep it around. Do not forget that Python 2 was released in 2000 and Python 3 was released almost a decade later. The general time scale makes worrying about the next release for many people, but for people who do they start considering other languages because that's important to them.
If/when the day comes that using Python 2 isn't realistic, I may go with 3, or I may choose a different language, depending on the project. I'll cross that bridge when I come to it.
Besides Java and Python already discussed, another big mess of a transition was from Qt 4 to Qt 5, where all the strings became unicode.