Glad to know you're aware of SemVer and considered it. That's all I wanted to accomplish. 
I disagree with your conclusion, but that's ok. I still love OctoPrint (It's amazing!) and will continue to use it, and I'm not at all upset with you or anyone here. I don't know why a few people seem to have been upset my my comment. 
To give but one example, when projects in the Node.js ecosystem drop support for an old version of Node, most consider that a breaking change, because it is not safe to blindly upgrade. Of course no software is perfect, but my interpretation of the SemVer rules is that as long as the major version hasn't changed, I should be able to accept any minor/patch upgrades without any danger to my project breaking, because the version number indicates that only feature-additions and/or bug fixes were made. If I happen to be running on an old version of Node (or Python) and upgrading to a new minor version of the library/app broke things, that would be a violation of (my interpretation of) SemVer.
Anyway, thanks again for a great project, and keep up the great work. 