Linux is a wonderful server OS, and in fact I do most of my development inside of a VirtualBox VM running Debian, but in order for me to move to a full Linux workflow, I need to use some proprietary software packages like Microsoft Office and Apple Keynote (while I find LibreOffice Writer to be a suitable replacement for Microsoft Word, Microsoft Excel fits my needs better than Calc, and Impress is behind both PowerPoint and Keynote).
In line with a paid, polished Linux experience, another thing that would be nice for me and other disgruntled Mac users is a Wine-like compatibility layer that allows Linux users to run Cocoa programs. There's already a project called Darling (http://www.darlinghq.org/introduction/) that has some of the basic functionality implemented. If this project had more contributors, then it could develop into a working solution for running my Mac programs.
My dream OS would have a Unix-like foundation (like Linux or FreeBSD) with an interface similar to Mac OS 8/9 (with various features from OS X added like Spotlight, Expose, and the Dock) and with Don Norman's UI advice (http://www.jnd.org/dn.mss/apples_products_are.html) taken seriously.
I'm actually interested in contributing to such efforts toward an alternative OS for disgruntled Mac users; I have experience with systems and kernel programming. If there is enough interest, maybe an alternative OS will materialize.